Glossary of chemistry terms

{{Short description|none}} {{TopicTOC-Chemistry}} This '''glossary of chemistry terms''' is a list of terms and definitions relevant to chemistry, including chemical laws, diagrams and formulae, laboratory tools, glassware, and equipment. Chemistry is a physical science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions; it features an extensive vocabulary and a significant amount of jargon.

''Note: All periodic table references refer to the IUPAC Style of the Periodic Table.''

{{compact TOC|side=yes|center=yes|nobreak=yes|seealso=yes|refs=yes|extlinks=yes}}

== A == {{glossary}} {{term|absolute zero}} {{defn|defn=A theoretical condition concerning a system at the lowest limit of the thermodynamic temperature scale, or zero {{gli|kelvins}}, at which the system does not emit or absorb energy (i.e. all {{gli|atoms}} are at rest). By extrapolating the {{gli|ideal gas law}}, the internationally agreed-upon value for absolute zero has been determined as {{convert|-273.15|C|F K}}.}}

{{term|absorption}} {{defn|no=1|The physical or chemical process by which a substance in one {{gli|state}} becomes incorporated into and retained by another substance of a different state. Absorption differs from {{gli|adsorption}} in that the first substance permeates the entire bulk of the second substance, rather than just adhering to the surface.}} {{defn|no=2|The process by which matter (typically {{gli|electrons}} bound in atoms) takes up the energy of {{gli|electromagnetic radiation}} and transforms it into any of various types of internal energy, such as thermal energy. This type of absorption is the principle on which {{gli|spectrophotometry}} is based.}}

{{term|accuracy}} {{defn|How close a measured value is to the actual or true value. Compare ''{{gli|precision}}''.}}

{{term|achiral}} {{defn|(of a {{gli|molecule}}) Having the geometric symmetry of being indistinguishable from its own mirror image; lacking {{gli|chirality}}.}}

{{term|acid}}{{anchor|acids}} {{defn|no=1|({{gli|Brønsted–Lowry acid}}) Any {{gli|chemical species}} or {{gli|molecular entity}} that acts as a {{gli|proton}} donor when reacting with another species, because it loses at least one proton ({{chem|H|+}}) which is then transferred or 'donated' to the other species, which by definition is a {{gli|Brønsted–Lowry base}}. When dissolved in an {{gli|aqueous solution}}, a proton donor which increases the concentration of {{gli|hydronium}} ion ({{chem|H|3|O|+}}) by transferring protons to water molecules may also be called an {{gli|Arrhenius acid}}. The term "acid", when not otherwise qualified, often refers implicitly to a Brønsted–Lowry acid.<ref name="Oxtoby8th">{{cite book |last1=Otoxby |first1=D. W. |last2=Gillis |first2=H. P. |last3=Butler |first3=L. J. |title=Principles of Modern Chemistry |date=2015 |publisher=Brooks Cole |isbn=978-1305079113 |page=617 |edition=8th}}</ref>}} {{defn|no=2|({{gli|Lewis acid}}) Any chemical species or molecular entity that acts as an {{gli|electron pair}} acceptor when reacting with another species, forming a {{gli|covalent bond}} by accepting a {{gli|lone pair}} of electrons donated by the other species, which is known as a {{gli|Lewis base}}. This definition was intended as a generalization of the Brønsted–Lowry definition by proposing that acid-base reactions are best viewed as reorganizations of electrons rather than transfers of protons, with the acid being a species that accepts electron pairs from another species either directly or by releasing protons ({{chem|H|+}}) into the solution, which then accept electron pairs from the other species. The Lewis definition is inclusive of many Brønsted–Lowry acids, though not all: most Lewis acids are not Brønsted–Lowry acids, and most Brønsted–Lowry acids are not Lewis acids.<ref name="Oxtoby8th"/>}} {{defn|no=3|Colloquially, any compound which, when dissolved in {{gli|water}}, yields a {{gli|pH}} of less than 7.0. The term "acid" is commonly used to refer to the entire aqueous {{gli|solution}}, whereas stricter definitions refer only to the acidic {{gli|solute}}.<ref name="Gold Book"/>}}

{{term|acid anhydride}} {{defn|Any chemical {{gli|compound}} derived by the removal of {{gli|water}} molecules from an {{gli|acid}}. Contrast ''{{gli|base anhydride}}''.}}

{{term|acid dissociation constant|acid dissociation constant (''K''a)}}{{anchor|acidity}} {{ghat|Also '''acid ionization constant''' or '''acidity constant'''.}} {{defn|A quantitative measure of the strength of an {{gli|acid}} in {{gli|solution}} expressed as an {{gli|equilibrium constant}} for a chemical {{gli|dissociation}} reaction in the context of {{gli|acid-base reaction|acid-base reactions}}. It is often given as its base-10 cologarithm, p''K''a.}}

{{term|acid–base extraction}} {{defn|A {{gli|chemical reaction}} in which {{gli|chemical species}} are separated from other {{gli|acids}} and {{gli|bases}}.}}

{{term|actinides}}{{anchor|actinide|actinoid}} {{ghat|Also '''actinoids'''.}} {{defn|The {{gli|period|periodic}} series of metallic elements with atomic numbers 89 to 103, from actinium through lawrencium.}}

{{term|activated complex}} {{defn|A structure that forms because of a collision between molecules while new bonds are formed.}}

{{term|activation energy}} {{defn|The minimum {{gli|energy}} which must be available to a chemical system with potential {{gli|reactants}} in order to result in a particular {{gli|chemical reaction}}.}}

{{term|activity series}} {{defn|See ''{{gli|reactivity series}}''.}}

{{term|acyclic}} {{defn|Containing only linear structures of atoms (particularly in {{gli|hydrocarbons}}).}}

{{term|addition reaction}} {{defn|In organic chemistry, a type of chemical reaction in which two or more molecules combine to make a larger one.}}

{{term|adduct}} {{defn|A distinct {{gli|chemical species}} that is the sole {{gli|product}} of an {{gli|addition reaction}} between two other distinct {{gli|reactant}} species, in which all of the atoms comprising the reactants are retained in the single product. Changes in connectivity may occur, but there is no loss of any of the original atoms and no gain of atoms that are not present in the reactant molecules. {{gli|stoichiometry|Stoichiometries}} other than 1:1 are also possible, e.g. a bis-adduct (2:1).<ref name="Gold Book"/>}}

{{term|adhesion}} {{defn|The tendency of dissimilar particles or surfaces to cling to one another as a result of {{gli|intermolecular forces}}. Contrast ''{{gli|cohesion}}''.}}

{{term|adsorption}} {{defn|The chemical {{gli|adhesion}} of atoms, ions, or molecules of one substance (either a {{gli|gas}}, {{gli|liquid}}, or dissolved {{gli|solid}}) to the surface of another substance, resulting in a film of the first substance being weakly bonded to the interface between the two substances. Adsorption differs from {{gli|absorption}} in that it is exclusively a surface phenomenon, while absorption involves entire volumes of materials.}}

{{term|aeration}} {{defn|The mixing of air into a {{gli|liquid}} or a {{gli|solid}}.}}

{{term|alcohol}}{{anchor|alcohols}} {{defn|Any {{gli|organic compound}} consisting of at least one {{gli|hydroxyl}} {{gli|functional group|group}} attached to a {{gli|saturated}} carbon atom. Alcohols have the general formula R–OH.}}

{{term|aldehyde}}{{anchor|aldehydes}} {{defn|defn=A {{gli|functional group}} and a class of organic compounds consisting of a {{gli|carbonyl}} group attached to a hydrogen atom and any other {{gli|side chain|R-group}}. Aldehydes have the general formula R–C(H)=O.}} thumb|right|350px|The skeletal formula for a generic '''{{gli|aldehyde}}''', where R denotes a variable carbon-containing substituent group

{{term|alkali metal}}{{anchor|alkali metals}} {{defn|Any of the metallic {{gli|elements}} belonging to {{gli|group|Group 1}} of the {{gli|periodic table}}: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).}}

{{term|alkaline earth metal}}{{anchor|alkaline earth metals}} {{defn|Any of the metallic {{gli|elements}} belonging to {{gli|group|Group 2}} of the {{gli|periodic table}}: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).}}

{{term|alkane}}{{anchor|alkanes}} {{ghat|Also '''paraffin'''.}} {{defn|Any fully {{gli|saturated}} {{gli|acyclic}} {{gli|hydrocarbon}},An acyclic saturated hydrocarbon containing only carbon and hydrogen atoms with only single carbon–carbon bonds; alkanes generally have the formula CnH2n+2. i.e. one in which all carbon–carbon bonds are {{gli|single bond|single bonds}}.}}

{{term|alkene}}{{anchor|alkenes}} {{ghat|Also '''olefin'''.}} {{defn|Any unsaturated {{gli|hydrocarbon}} containing at least one carbon–carbon {{gli|double bond}}.}}

{{term|alkoxy}} {{defn|A functional group of the form R–O–, derived from an alcohol by removal of the hydrogen atom from the hydroxyl group.}}

{{term|alkyl}}{{anchor|alkyl}} {{defn|The {{gli|substituent}} form of an {{gli|alkane}}, i.e. any alkane missing a hydrogen atom. The term may be used to broadly describe many different {{gli|functional groups}}, e.g. a {{gli|methyl}}, {{gli|ethyl}}, or {{gli|propyl}} group.}}

{{term|alkyne}}{{anchor|alkynes|acetylenes}} {{ghat|Also '''acetylene'''.}} {{defn|Any unsaturated {{gli|hydrocarbon}} containing at least one carbon–carbon {{gli|triple bond}}.}}

{{term|allomer}}{{anchor|allomers}} {{defn|A substance that differs in chemical composition but has the same {{gli|crystal|crystalline}} structure as another substance.}}

{{term|allotrope}}{{anchor|allotropes}} {{defn|Any of a variety of different structural forms of the same element, as with {{gli|carbon}}, whose allotropes include diamonds, graphite, and fullerene.}}

{{term|alloy}}{{anchor|alloys}} {{defn|A {{gli|mixture}} of elements where atleast one is a metal, which in combination exhibit a {{gli|metallic bonding}} character. Common examples include bronze, brass, and pewter.}}

{{term|amalgam}} {{defn|Any {{gli|alloy}} of mercury with another {{gli|metal}}.}}

{{term|ambident}} {{defn|A {{gli|molecule}} or {{gli|functional group}} that has two alternative and interacting reaction sites, to either of which a {{gli|bond}} may be made during a {{gli|reaction}}.}}

{{term|ammoniacal}} {{defn|Describing a {{gli|solution}} in which the {{gli|solvent}} is {{gli|aqueous}} ammonia.<ref name="Daintith">{{cite book |editor1-last=Daintith |editor1-first=John |title=A Dictionary of Chemistry |date=2004 |publisher=Oxford University Press |location=Oxford |isbn=0-19-860918-3 |edition=5th |url=https://openlibrary.org/works/OL18318889W/A_dictionary_of_chemistry?edition=ia%3Adictionaryofchem0000unse_r3p4}}</ref>}}

{{term|amount of substance}}{{anchor|amount}} {{ghat|Also '''enplethy''', '''chemical amount''', or simply '''amount'''.}} {{defn|The number of discrete particles (such as {{gli|molecules}}, {{gli|atoms}}, {{gli|ions}}, {{gli|electrons}}, or any other atomic-scale entity) in a given sample of {{gli|matter}}, divided by the {{gli|Avogadro's number|Avogadro constant}}. The {{gli|SI}} unit for amount of substance is the {{gli|mole}} (mol).}}

{{term|amphipathic}} {{defn|(of a {{gli|molecule}}) Composed of both {{gli|hydrophilic}} and {{gli|hydrophobic}} groups; e.g. {{gli|wetting agents}} and membrane lipids.<ref name="McGraw-Hill">{{cite book |title=Dictionary of Chemistry |date=2003 |publisher=McGraw-Hill |location=New York |isbn=0-07-141046-5 |edition=2nd |url=https://openlibrary.org/works/OL14995635W/Dictionary_of_Chemistry?edition=ia%3Adictionaryofchem00mcgr_1}}</ref>}}

{{term|amphoteric}} {{ghat|Also '''amphiprotic'''.}} {{defn|(of a {{gli|chemical species}}) Tending to behave both as an {{gli|acid}} and as a {{gli|base}}, depending upon the medium in which the species is situated; e.g. sulfuric acid (H2SO4) is a {{gli|strong acid}} in water but behaves more like a base in {{gli|superacids}}.}}

{{term|amyl}} {{defn|A common non-systematic name for a {{gli|pentyl}} group.}}

{{term|analyte}}{{anchor|analytes}} {{defn|The specific substance or chemical constituent that is of interest in a {{gli|analytical chemistry|chemical analysis}}.}}

{{term|analytical chemistry}} {{defn|The branch of chemistry which studies and makes use of instruments and methods to separate, quantify, and identify chemical substances, both by classical {{gli|wet chemistry}} techniques such as {{gli|precipitation}}, {{gli|extraction}}, {{gli|distillation}}, and observational analysis, and by modern instrumental techniques such as {{gli|chromatography}}, {{gli|spectroscopy}}, and {{gli|electrochemistry}}.}}

{{term|ångström (Å)}} {{defn|A non-{{gli|SI}}, metric unit of length equal to {{val|e=-10}} metre, i.e. {{frac|10000000000}} of a metre or 0.1 nanometre. The angstrom is commonly used in the natural sciences to express microscopic or atomic-scale distances, including the sizes of atomic nuclei, wavelengths of electromagnetic radiation, and lengths of chemical bonds (e.g. the {{gli|covalent radius}} of a chlorine atom averages about 1 angstrom).}}

{{term|anhydrous}} {{defn|Having or containing no {{gli|water}} molecules, referring especially to {{gli|water of crystallization|water of hydration}}.<ref name="McGraw-Hill"/> Because many processes in chemistry are impeded in the presence of water, it is often of critical importance that water-free reagents and techniques are used. Anhydrous compounds tend to gradually {{gli|hygroscopic|absorb water}} from the atmosphere. Contrast ''{{gli|hydrous}}''.}}

{{term|anion}}{{anchor|anions|anionic}} {{defn|A negatively charged {{gli|ion}}; i.e. an atom or molecule with a net negative electric charge caused by an excess of {{gli|electrons}} compared to {{gli|protons}}.}}

{{term|annulation}} {{defn|The formation of a {{gli|cyclic}} compound or ring structure from one or several acyclic precursors; or a reaction involving the addition of a ring structure to another molecule via two new bonds.<ref name="Gold Book"/>}}

{{term|anode}}{{anchor|anodes}} {{defn|no=1|An {{gli|electrode}} through which the conventional electric current (the flow of positive charges) enters into a {{gli|polarity|polarized}} electrical circuit.}} {{defn|no=2|The wire or plate of an {{gli|electrochemical cell}} having an excess positive charge. Negatively charged {{gli|anions}} always move toward the anode. Contrast ''{{gli|cathode}}''.}}

{{term|anomer}} {{defn|Either of a pair of {{gli|cyclic}} {{gli|hemiacetal}} or {{gli|hemiketal}} {{gli|saccharides}} that are {{gli|epimers}} of each other, differing at only one carbon {{gli|stereocenter}}, specifically the carbon that bears the {{gli|aldehyde}} or {{gli|ketone}} functional group in the compound's acyclic, open-chain configuration, known as the '''anomeric carbon'''.}}

{{term|aprotic}} {{defn|(of a chemical species) Not {{gli|protic}}; i.e. not capable of acting as a {{gli|proton}} donor or readily yielding of protons ({{chem|H|+}}) in solution.}}

{{term|aqua regia}} {{defn|A liquid {{gli|mixture}} of nitric acid (HNO3) and hydrochloric acid (HCl), optimally in a {{gli|molar concentration|molar}} ratio of 1:3, so named by historical alchemists because it is capable of {{gli|dissolving}} the {{gli|noble metals}} gold and platinum.}}

{{term|aquation}} {{defn|The process by which {{gli|water}} molecules {{gli|solvate}} or form {{gli|coordination complexes}} with {{gli|ions}}.<ref name="Daintith"/>}}

{{term|aqueous solution}}{{anchor|aqueous solutions|aqueous}} {{defn|A {{gli|solution}} in which the {{gli|solvent}} is {{gli|water}}. It is denoted in chemical equations by appending ''(aq)'' to a {{gli|chemical formula}}.}}

{{term|aromaticity}}{{anchor|aromatic}} {{defn|A chemical property of conjugated rings of atoms, such as {{gli|benzene}}, which results in unusually high stability. Such rings are said to be {{gli|aromatic}}.}}

{{term|Arrhenius acid}} {{defn|Any substance that, when dissolved in {{gli|water}}, increases the concentration of {{gli|hydron|{{chem|H|+}}}} {{gli|ions}}, or, more correctly, of {{gli|hydronium}} ions ({{chem|H|3|O|+}}), in the resulting {{gli|aqueous solution}}.<ref name="Oxtoby8th">{{cite book |last1=Otoxby |first1=D. W. |last2=Gillis |first2=H. P. |last3=Butler |first3=L. J. |title=Principles of Modern Chemistry |date=2015 |publisher=Brooks Cole |isbn=978-1305079113 |page=617 |edition=8th}}</ref> The definition is similar to that of a {{gli|Brønsted–Lowry acid}}. Contrast ''{{gli|Arrhenius base}}''.}}

{{term|Arrhenius base}} {{defn|Any substance that, when dissolved in {{gli|water}}, increases the concentration of {{gli|hydroxide|{{chem|OH|-}}}} {{gli|ions}}, or, alternatively, decreases the concentration of {{gli|hydronium}} ions ({{chem|H|3|O|+}}), in the resulting {{gli|aqueous solution}}.<ref name="Oxtoby8th"/> The definition is similar to that of a {{gli|Brønsted–Lowry base}}. Contrast ''{{gli|Arrhenius acid}}''.}}

{{term|aryl}} {{defn|Any {{gli|functional group}} or {{gli|substituent}} derived from an {{gli|aromaticity|aromatic ring}}, such as phenyl or naphthyl. The symbol ''Ar'' is often used as a placeholder for a generic aryl group in structural diagrams.}}

{{term|atmolysis}} {{defn|The separation of a {{gli|mixture}} of {{gli|gases}} by exploiting their different rates of {{gli|diffusion}}, usually by allowing the gases to diffuse through the walls of a porous partition or membrane.<ref name="Daintith"/>}}

{{term|atom}}{{anchor|atoms}} {{defn|A chemical element in its smallest form, made up of {{gli|protons}} and {{gli|neutrons}} within the nucleus and {{gli|electrons}} circling the nucleus.}} thumb|right|350px|An '''{{gli|atom}}''' with {{gli|protons}}, {{gli|neutrons}}, and {{gli|electrons}} labelled

{{term|atomic mass}} {{defn|The {{gli|mass}} of an {{gli|atom}}, typically expressed in {{gli|daltons}} and nearly equivalent to the {{gli|mass number}} multiplied by one dalton.}}

{{term|atomic mass unit}} {{defn|See ''{{gli|dalton}}''.}}

{{term|atomic number (''Z'')}}{{anchor|atomic number|atomic numbers}} {{ghat|Also '''proton number'''.}} {{defn|The number of {{gli|protons}} found in the {{gli|nucleus}} of an {{gli|atom}} of a given {{gli|chemical element}}. It is identical to the {{gli|charge number}} of the nucleus and is used in the {{gli|periodic table}} to uniquely identify each chemical element.}}

{{term|atomic orbital}}{{anchor|atomic orbitals}} {{defn|Any region in which one or more {{gli|electrons}} may be found in an individual {{gli|atom}} (as opposed to that within {{gli|molecular orbital|a molecule}}).}}

{{term|atomic weight}} {{defn|See ''{{gli|relative atomic mass}}''.}}

{{term|atomicity}} {{defn|The total number of {{gli|atoms}} present in a single {{gli|molecule}} of a given substance; e.g. ozone (O3) has an atomicity of 3, while benzene (C6H6) has an atomicity of 12.<ref name="Daintith"/>}}

{{term|autoignition temperature}} {{ghat|Also '''kindling point'''.}} {{defn|The lowest temperature at which a given substance will spontaneously ignite in a normal atmosphere without an external source of ignition such as a flame or spark, i.e. when the ambient temperature is sufficiently high to provide the {{gli|activation energy}} needed for {{gli|combustion}}. Substances which spontaneously ignite at naturally occurring temperatures are termed ''pyrophoric''. Compare ''{{gli|ignition temperature}}''.}}

{{term|term=Avogadro constant|content=Avogadro constant (''N''A)}} {{defn|The ratio of the number of discrete constituent particles (such as {{gli|molecules}}, {{gli|atoms}}, or {{gli|ions}}) to the {{gli|amount of substance|amount of a substance}}, defined as exactly {{val|6.02214076|e=23|u=mol-1}}.}}

{{term|Avogadro number}} {{defn|The number of discrete constituent particles in one {{gli|mole}} of a substance, defined as exactly 6.02214076{{e|23}}. This dimensionless number differs from the {{gli|Avogadro constant}} in that it has no unit.}}

{{term|Avogadro's law}} {{defn|}} {{term|azeotrope}} {{defn|A {{gli|mixture}} of {{gli|liquids}} whose {{gli|chemical composition}} is unchanged by {{gli|distillation}}.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== B == {{glossary}} {{term|balance}} {{defn|}}

{{term|backbone}} {{ghat|Also '''main chain'''.}} {{defn|The primary or most structurally significant portion of a {{gli|molecule}} with respect to its other parts, {{gli|functional groups}}, {{gli|moieties}}, or {{gli|substituents}}; or, in the case of a {{gli|polymer}}, that linear chain of atoms to which all other chains, long or short or both, may be regarded as being {{gli|pendant}} or as {{gli|side chains}}. Where two or more chains might equally be considered the backbone, the one which permits the simplest representation of the molecule in chemical formulae and nomenclature is considered the backbone.<ref name="Gold Book"/>}}

{{term|base}}{{anchor|bases}} {{defn|A substance that accepts a {{gli|proton}} and has a {{gli|pH}} above 7.0. A common example is sodium hydroxide (NaOH).}}

{{term|base anhydride}} {{defn|An {{gli|oxide}} of a group I or II metal element.}}

{{term|beaker}}{{anchor|beakers}} {{defn|A cylindrical vessel or container with a flat bottom, most commonly a type of glassware, widely used in laboratories for a variety of purposes, such as preparing, holding, containing, collecting, or volumetrically measuring chemicals, samples, or solutions, or as a chamber in which a {{gli|chemical reaction}} occurs. Beakers are distinguished from {{gli|flasks}} by having straight rather than sloping sides; most beakers also have a small spout in the rim to aid pouring.}}

{{term|term=Beer–Lambert law|content=Beer–Lambert law}} {{ghat|Also '''Beer–Lambert–Bouguer law''' or simply '''Beer's law'''.}} {{defn|defn=A chemical law stating that the amount of light absorbed by a solution is proportional to the solution's concentration; or more specifically that the absorbance (<math>A</math>) of a beam of radiation by a homogeneous isotropic medium is directly proportional to the absorption path length (<math>l</math>) and to the concentration (<math>c</math>) or the pressure (<math>p</math>) of the absorbing species. This is usually expressed with the equation <math>A = \epsilon cl</math>, in which <math>\epsilon</math> is a proportionality constant called the molar absorption coefficient.<ref name="Gold Book"/>}}

{{term|biochemistry}} {{defn|The study of the chemistry of biological systems and organisms.}}

{{term|Bohr model}} {{ghat|Also '''Rutherford–Bohr model'''.}} {{defn|A model of the general structure of the {{gli|atom}} proposed by Niels Bohr and Ernest Rutherford in 1913, featuring a small, dense {{gli|nucleus}} of {{gli|nucleon|positively charged particles}} surrounded by {{gli|orbital|orbiting}} {{gli|electrons}}, which are attracted to the nucleus by electrostatic forces. This interpretation replaced several earlier hypotheses and quickly became the prevailing standard model for depicting atomic structure.}}

{{term|boiling}} {{ghat|Also '''ebullition'''.}} {{defn|A more rapid, highly energetic form of {{gli|vaporization}}, in which a substance undergoes a {{gli|phase transition}} from {{gli|liquid}} to {{gli|gas}}, as contrasted with the much slower process of vaporization. Boiling occurs when a liquid is heated to its {{gli|boiling point}}, above which the liquid's internal {{gli|vapor pressure}} exceeds the pressure exerted upon it by the surrounding atmosphere, causing the gaseous phase to rapidly and often violently separate from the liquid phase.}}

{{term|boiling flask}} {{ghat|Also '''Florence flask'''.}} {{defn|A type of {{gli|flask}}, usually made of glass, with a large round body, long neck, and flat bottom, designed especially for heating, {{gli|boiling}}, and {{gli|distilling}} liquids and to make swirling easy. See also ''{{gli|round-bottom flask}}''.}}

{{term|boiling point}}{{anchor|boiling points}} {{ghat|Also '''vaporization point'''.}} {{defn|The {{gli|temperature}} at which a substance changes {{gli|state}} from a {{gli|liquid}} to a {{gli|gas}} (or {{gli|vapor}}). It depends on {{gli|pressure}} and is usually specified for a given substance under {{gli|standard temperature and pressure|standard conditions}}.}}

{{term|boiling-point elevation}} {{defn|The process by which a substance's {{gli|boiling point}} is elevated by adding another substance.}}

{{term|bond}}{{anchor|bonds|chemical bonds|bonding|chemical bonding|bonded}} {{defn|Any persistent attraction between {{gli|atoms}}, {{gli|ions}}, or {{gli|molecules}} that enables the formation of {{gli|chemical compounds}}. Bonds are created as a result of a wide variety of electrochemical forces, whose strengths can vary considerably; they are broken when these forces are overcome by other forces. The types, strengths, and quantities of bonds holding together chemical substances dictate the structure and bulk properties of {{gli|matter}}.}}

{{term|Boyle's law}} {{defn|For a given mass of gas at constant temperature, the volume varies inversely with the pressure.}}

{{term|bridge}} {{defn|A {{gli|chemical bond}} between {{gli|valence electrons}}, or an atom or unbranched chain of atoms connecting two different parts of the same molecule; i.e. an intramolecular bond linking different {{gli|moieties}} or {{gli|functional groups}}.<ref name="Gold Book"/>}}

{{term|bridgehead}}{{anchor|bridgeheads}} {{defn|Either of the two tertiary atoms which by bonding to each other form an intramolecular {{gli|bridge}}.<ref name="Gold Book"/>}}

{{term|Brønsted–Lowry acid}}{{anchor|Bronsted-Lowry acid}} {{defn|Any chemical species that readily donates a {{gli|proton}}.}}

{{term|Brønsted–Lowry base}}{{anchor|Bronsted-Lowry base}} {{defn|Any chemical species that readily accepts a {{gli|proton}}.}}

{{term|buffered solution}}{{anchor|buffer|buffers}} {{ghat|Also simply called a '''buffer'''.}} {{defn|An {{gli|aqueous solution}} consisting of a weak {{gli|acid}} and its {{gli|conjugate base}} or a weak {{gli|base}} and its {{gli|conjugate acid}} that resists changes in {{gli|pH}} when strong acids or bases are added.}}

{{term|bumping}} {{defn|A phenomenon in which a homogeneous liquid raised to its {{gli|boiling point}} becomes {{gli|superheating|superheated}} and, upon {{gli|nucleation}}, rapidly boils to the gas phase, resulting in a violent expulsion of the liquid from the container; in extreme cases, the container itself may shatter. Frequent stirring, the use of an appropriate container, and the use of boiling chips can help prevent bumping.}}

{{term|bung}} {{ghat|Also '''stopper''' or '''cork'''.}} {{defn|A cylindrical or conical plug or closure used to seal a container such as a bottle, tube, {{gli|flask}}, or barrel.}}

{{term|burette}} {{ghat|Also spelled '''buret'''.}} {{defn|Glassware used to dispense specific amounts of {{gli|liquid}} when precision is necessary (e.g. during {{gli|titrations}} and {{gli|resource dependent reaction|resource-dependent reactions}}).}}

{{term|butyl}} {{defn|The {{gli|alkyl}} {{gli|functional group}} derived from either of the two isomers of butane, with the generic chemical formula –{{chem|C|4|H|9}}. It may occur as a {{gli|substituent}} in organic compounds or exist independently as an ion or radical. In {{gli|IUPAC}} nomenclature, the presence of a butyl substituent is indicated with the prefix ''butyl'' in the name of the compound, or with the abbreviation ''Bu'' in chemical formulae; e.g. butyl alcohol (butanol), which may occur in any of five different isomeric forms depending on the arrangement of the four carbon atoms, is often written with the generic formula {{chem|CH|4|CH|9|OH}} or {{chem|Bu|OH}}.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== C == {{glossary}} {{term|calorific value}} {{defn|A measure of the {{gli|heat}} per unit {{gli|mass}} produced by complete {{gli|combustion}} of a given substance, usually expressed in {{gli|joule|megajoules}} per {{gli|kilogram}} (MJ/kg) or in kilojoules per gram (kJ/g).<ref name="Daintith"/>}}

{{term|calorimeter}} {{defn|Any of various devices used to measure thermal properties (i.e. {{gli|heat}}), such as {{gli|calorific value|calorific values}} or heats of chemical reactions.<ref name="Daintith"/>}}

{{term|calx}} {{defn|A metal {{gli|oxide}} formed by heating an ore in air.<ref name="Daintith"/>}}

{{term|carbanion}}{{anchor|carbanions}} {{defn|Any organic {{gli|ion}} with a negative charge on a {{gli|carbon}} atom, i.e. an ion of the general formula {{chem|R|3|C|−}}. Carbanions are frequently {{gli|reactive intermediate|intermediate species}} in certain organic reactions.<ref name="Daintith"/> Contrast ''{{gli|carbocation}}''.}}

{{term|carbide}} {{defn|A class of {{gli|interstitial compounds}} composed of {{gli|carbon}} bonded to a particular {{gli|metal}} (usually a large-radius {{gli|transition metal}}) in a densely packed crystal lattice, where the carbon atoms occupy interstices between the metal atoms; e.g. tungsten carbide (WC).}}

{{term|carbonization}}{{anchor|carbonizes|carbonizing|carbonized}} {{defn|no=1|The conversion of {{gli|organic compounds}}, such as those found in biological organisms, into other forms of carbon or carbonic residues by heating or burning, or during fossilization.}} {{defn|no=2|The process of coating a substance with carbon residues such as charcoal, or of causing a substance to become scorched, blackened, or charred.}}

{{term|carbonyl}} {{defn|no=1|content=A {{gli|functional group}} composed of a carbon atom {{gli|double-bonded}} to an oxygen atom, with the formula <chem>C=O</chem>. Carbonyl groups are common to many classes of organic compounds and are also a part of many larger functional groups.}} {{defn|no=2|An {{gli|inorganic}} or {{gli|organometallic chemistry|organometallic}} {{gli|coordination complex}} with carbon monoxide as a {{gli|ligand}} (e.g. a metal carbonyl).}}

{{term|carboxylic acid}}{{anchor|carboxylic acids}} {{defn|A class of {{gli|organic acids}} and a {{gli|functional group}} consisting of a {{gli|carboxyl}} group attached to a {{gli|substituent}} group. Carboxylic acids have the general formula <chem>R-COOH</chem> (also written as <chem>R-CO2H</chem>), where <chem>R</chem> can be an {{gli|alkyl}}, {{gli|alkenyl}}, {{gli|aryl}}, or any other carbon-containing substituent.}} thumb|right|350px|The skeletal formula for a generic '''{{gli|carboxylic acid}}''', with ''{{font|R|font=times new roman|size=125%}}'' denoting a variable carbon-containing substituent group

{{term|CAS Registry Number (CAS RN)}} {{ghat|Also simply '''CAS Number'''.}} {{defn|A unique numerical identifier assigned by the Chemical Abstracts Service (CAS) to every {{gli|chemical substance}} described in the open scientific literature, including more than 182 million {{gli|organic}} and {{gli|inorganic}} compounds, {{gli|minerals}}, {{gli|isotopes}}, {{gli|alloys}}, {{gli|polymers}}, and {{gli|mixtures}}, as well as so-called "UVCBs" (substances of unknown or variable composition, complex reaction products, or biological origin). CAS numbers are an internationally recognized standard used by scientists, industries, and regulatory bodies.<ref name=crc>{{cite web|author=American Chemical Society|author-link=American Chemical Society|title=CAS Registry and CASRNs|url=http://www.cas.org/expertise/cascontent/registry/regsys.html#q2|access-date=25 July 2009|archive-url=https://web.archive.org/web/20080725010848/http://www.cas.org/expertise/cascontent/registry/regsys.html#q2#q2|archive-date=25 July 2008|url-status=dead|df=dmy-all}}</ref>}}

{{term|catalyst}}{{anchor|catalysts}} {{defn|Any element or compound that facilitates an increase in the {{gli|reaction rate|rate}} of a {{gli|chemical reaction}} but which is not consumed or destroyed during the reaction. It is considered both a {{gli|reactant}} and a {{gli|product}} of the reaction.}}

{{term|cathode}}{{anchor|cathodes}} {{defn|An {{gli|electrode}} from which the conventional electric current (the flow of positive charges) exits a {{gli|polarity|polarized}} electrical circuit. Positively charged {{gli|cations}} always move toward the cathode, though the cathode's polarity can be positive or negative depending on the type of electrical device and how it is being operated. Contrast ''{{gli|anode}}''.}}

{{term|cation}}{{anchor|cations|cationic}} {{defn|A positively charged {{gli|ion}}.}}

{{term|cell potential}} {{defn|The force in a galvanic cell that pulls electrons through a reducing agent to an oxidizing agent.}}

{{term|centrifugation}} {{defn|A laboratory technique which involves the application of centrifugal force to separate particles from a {{gli|solution}} according to their size, shape, and density. Larger and/or denser substances migrate away from the axis of a {{gli|centrifuge}}, while smaller and/or less dense substances migrate towards the axis.}}

{{term|centrifuge}} {{defn|A device used to separate substances based on size, shape, and density by {{gli|centrifugation}}, or the rotation of vessels containing the substances around a centred axis at extremely high velocities.}}

{{term|charge number}} {{defn|defn=A quantized value of {{gli|electric charge}} calculated as the electric charge in {{gli|coulombs}} divided by the elementary-charge constant, or ''z'' = ''q''/''e''. Charge numbers for {{gli|ions}} are denoted in superscript (e.g. Na+ indicates a sodium ion with a charge number of positive one). {{gli|atomic number|Atomic numbers}} are charge numbers of {{gli|nucleus|atomic nuclei}}.}}

{{term|Charles's law}} {{defn|A classical gas law which states that when the {{gli|pressure}} on a sample of a dry gas is held constant, the Kelvin temperature is directly proportional to its {{gli|volume}}.}}

{{term|chelation}} {{defn|A type of {{gli|bonding}} involving the formation of two separate {{gli|coordinate covalent bonds}} between a {{gli|denticity|polydentate}} {{gli|ligand}} and a single central {{gli|metal}} {{gli|ion}}. The ligand is usually an {{gli|organic compound}} called a ''chelant'' or ''{{gli|chelating agent}}''.}}

{{term|chemical}} {{defn|See ''{{gli|chemical species}}'' and ''{{gli|chemical compound}}''.}}

{{term|chemical bond}} {{defn|See ''{{gli|bond}}''.}}

{{term|chemical composition}}{{anchor|chemical compositions|composition|compositions}} {{defn|The identity and relative number of the {{gli|elements}} that make up a {{gli|chemical compound}}, which can often be expressed with a {{gli|chemical formula}}.}}

{{term|chemical compound}} {{defn|See ''{{gli|compound}}''.}}

{{term|chemical decomposition}}{{anchor|decomposition}} {{defn|The breakdown of a single particle or entity (such as a {{gli|molecule}} or {{gli|reactive intermediate}}) into two or more fragments, or a {{gli|chemical reaction}} in which two or more {{gli|products}} are formed from a single {{gli|reactant}}. Contrast ''{{gli|chemical synthesis}}''.}}

{{term|chemical element}} {{defn|See ''{{gli|element}}''.}}

{{term|chemical formula}} {{defn|Any of various means of concisely displaying information about the {{gli|chemical composition}} of a {{gli|compound}} or {{gli|molecule}} using letters, numbers, and/or typographical symbols. Chemical formulas, such as {{gli|empirical formula|empirical}} and {{gli|molecular formulas}}, can only indicate the identities and numerical proportions of the atoms in a compound and are therefore more limited in descriptive power than {{gli|chemical nomenclature|chemical names}} and {{gli|structural formulas}}.}}

{{term|chemical law}} {{defn|A law of nature relevant to {{gli|chemistry}}, such as the {{gli|law of conservation of mass}}.}}

{{term|chemical process}} {{defn|no=1|Any method or means of changing one or more {{gli|chemical species|chemicals}} or {{gli|chemical compounds}} in any way, either naturally or artificially, spontaneously or by the actions of external forces.}} {{defn|no=2|In chemical engineering, any method used on an industrial scale (especially in manufacturing) to change the composition of one or more chemicals or materials.}}

{{term|chemical reaction}}{{anchor|chemical reactions|reaction|reactions|react|reacting|reacted}} {{defn|The change of one or more {{gli|substances}} into one or more different substances.}}

{{term|chemical species}}{{anchor|species}} {{ghat|Also simply called a '''chemical'''.}} {{defn|A {{gli|chemical substance}} or ensemble of substances composed of chemically identical molecular entities which can explore the same set of molecular energy levels on a characteristic or delineated time scale.}}

{{term|chemical substance}}{{anchor|chemical substances|substance|substances|pure substance|pure substances}} {{ghat|Also '''pure substance''' or simply '''substance'''.}} {{defn|A form of {{gli|matter}} that has constant {{gli|chemical composition}} and characteristic {{gli|physical property|properties}} and which cannot be separated into simpler components by purely physical methods (i.e. without breaking {{gli|bond|chemical bonds}}). It is often called a ''pure substance'' to distinguish it from a {{gli|mixture}}.}}

{{term|chemical synthesis}}{{anchor|synthesis}} {{defn|The artificial execution of one or more {{gli|chemical reactions}} in order to obtain one or more {{gli|products}}. In modern laboratory contexts, specific chemical syntheses are both reliable and reproducible.}}

{{term|chemistry}} {{defn|The scientific discipline that studies {{gli|chemical substances}}, {{gli|compounds}}, and {{gli|molecules}} composed of {{gli|atoms}} of various {{gli|chemical elements}}, as well as their {{gli|compositions}}, structures, properties, behaviors, and the changes they undergo during {{gli|reactions}} with other substances.}}

{{term|chirality}}{{anchor|chiral}} {{defn|A property of asymmetry in which a {{gli|molecule}} or {{gli|ion}} is distinguishable from its mirror image such that it cannot be {{gli|superposability|superposed}} upon it by any combination of geometric rotations, translations, or some {{gli|conformational isomerism|conformational}} changes.<ref>''Organic Chemistry'' (3rd Edition) Marye Anne Fox, James K. Whitesell Jones & Bartlett Publishers (2004) {{ISBN|0763721972}}</ref><ref>{{GoldBookRef|title=Chirality|file=C01058}}</ref> Such a molecule or ion is said to be ''chiral'', and exists in two forms, known as {{gli|enantiomers}}, which are {{gli|stereoisomers}} of each other; these forms are distinguished as either "right-handed" or "left-handed" by their {{gli|absolute configuration}} or some other criterion. Several different types of asymmetry can give rise to chirality, most commonly when molecules possess stereogenic elements such as one or more {{gli|stereocenters}} ({{gli|central chirality}}), a stereogenic axis ({{gli|axial chirality}}), or a stereogenic plane ({{gli|planar chirality}}); additionally, the inherent curvature of a molecule can cause it to possess {{gli|inherent chirality}}.}} thumb|right|350px|Structural diagrams of two '''{{gli|chirality|chiral}}''' molecules, the non-superposable mirror-image enantiomers (''S'')-alanine (left) and (''R'')-alanine (right). Though they have identical {{gli|structural formula|structural formulas}} and the same physical properties, they are nevertheless different chemicals, and react differently with other chiral compounds.

{{term|chromatography}} {{defn|Any of a variety of laboratory methods designed to separate a heterogeneous mixture into its component chemical species by first dissolving the mixture in a gas or liquid solvent called the ''mobile phase'' and then passing it through a system such as a chromatography column or a capillary tube upon which a material called the ''stationary phase'' is fixed. The different species present in the mixture have different affinities for and retention times upon the stationary phase, causing them to separate from the rest of the species in the moving fluid at characteristic rates. This phenomenon is exploited both to detect or measure the relative proportions of analytes present in a mixture, and to purify specific compounds.}}

{{term|chromometer}} {{defn|See ''{{gli|colorimeter}}''.}}

{{term|cohesion}} {{defn|The tendency of similar particles or surfaces to cling to one another as a result of {{gli|intermolecular forces}}. Contrast ''{{gli|adhesion}}''.}}

{{term|colligative property}} {{defn|Any property of a {{gli|solution}} that depends upon the ratio of the number of {{gli|solute}} particles to the number of {{gli|solvent}} particles in the solution, and not on the nature of the {{gli|chemical species}} present. Examples include {{gli|osmotic pressure}}, {{gli|freezing-point depression}}, and {{gli|boiling-point elevation}}.}}

{{term|colloid}}{{anchor|colloids|colloidal}} {{defn|A {{gli|mixture}} in which microscopic {{gli|insoluble}} particles are {{gli|suspended}} within and evenly {{gli|dispersed}} throughout another substance, usually a liquid but sometimes inclusive of aerosols and gels. Thus a colloid contains a dispersed phase and a continuous phase. Many milks are colloids.}}

{{term|color standard}} {{defn|A liquid {{gli|solution}} of known chemical composition and concentration, and hence of known and standardized color, used as a reference in the optical analysis of samples of unknown strength.<ref name="McGraw-Hill"/>}}

{{term|color test}} {{defn|The quantitative analysis of a substance by comparing the intensity of the color produced when the substance is exposed to a {{gli|reagent}} with a {{gli|color standard|standard color}} produced similarly in a solution of known strength.<ref name="McGraw-Hill"/>}}

{{term|colorimeter}} {{ghat|Also '''chromometer'''.}} {{defn|Any instrument used for {{gli|color test|color measurement}} based on optical comparison with {{gli|color standard|standard colors}},<ref name="Gold Book"/> particularly a device used in {{gli|colorimetry}} that measures the {{gli|absorbance}} of specific wavelengths of light by a given solution in order to determine the {{gli|concentration}} of a known {{gli|solute}} in the solution, by application of the principle that {{gli|Beer–Lambert law|solute concentration is directly proportional to absorbance}}.}}

{{term|combustion}}{{anchor|combust|combusting}} {{defn|An {{gli|exothermic process|exothermic}} reaction between an {{gli|oxidant}} and a fuel that produces large amounts of heat and often light.}} thumb|right|350px|An example of large-scale, rapid '''{{gli|combustion}}'''

{{term|Commission on Isotopic Abundances and Atomic Weights (CIAAW)}} {{defn|}}

{{term|complex}} {{defn|A molecular entity formed by loose {{gli|association}} between two or more component molecular entities ({{gli|ionic}} or uncharged), or the corresponding {{gli|chemical species}}. The {{gli|bonding}} between the components is normally weaker than in a {{gli|covalent bond}}.<ref name="Gold Book">IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). Online version (2019-) created by S. J. Chalk. {{ISBN|0-9678550-9-8}}. {{doi|10.1351/goldbook}}.</ref> See also ''{{gli|coordination complex}}''.}}

{{term|compound}}{{anchor|compounds|chemical compound|chemical compounds}} {{defn|A {{gli|substance}} that is made up of two or more {{gli|bond|chemically bonded}} {{gli|elements}}.}}

{{term|Compton rule}} {{defn|An empirical law of {{gli|physical chemistry}} which states that the {{gli|heat of fusion}} of a given {{gli|element}} multiplied by its {{gli|atomic weight}} and then divided by its {{gli|melting point}} in {{gli|kelvin}} is always equal to approximately 2.<ref name="McGraw-Hill"/>}}

{{term|concentration}}{{anchor|concentrations}} {{defn|The quantity or abundance of a constituent of a {{gli|mixture}} per unit quantity of that mixture; e.g. the {{gli|amount}}, in {{gli|moles}}, of a dissolved {{gli|solute}} per unit {{gli|volume}} of a {{gli|solution}}, a measure known as {{gli|molar concentration}} or molarity. Several different definitions of concentration are widely used in chemistry, including molar concentration, {{gli|mass concentration}}, and {{gli|volume concentration}}.}}

{{term|condensation}}{{anchor|condense|condenses|condensing|condensed}} {{defn|The {{gli|phase transition}} of a substance from a {{gli|gas}} to a {{gli|liquid}}.}}

{{term|condosity}} {{defn|A comparative measurement of the electrical conductivity of a {{gli|solution}} defined as the {{gli|molar concentration}} of a sodium chloride (NaCl) solution that has the same specific electrical conductance as the solution under test. It is typically expressed in units of {{gli|mole|moles}} per {{gli|litre}} (or per some other unit of volume).}}

{{term|conductivity}} {{defn|See ''{{gli|electrical conductivity}}'' and ''{{gli|thermal conductivity}}''.}}

{{term|conductor}}{{anchor|conductors|conducting|conducted}} {{defn|Any object or material that allows the flow of an {{gli|electric current}} in one or more directions. Contrast ''{{gli|insulator}}''.}}

{{term|conformation}}{{anchor|conformations}} {{defn|The spatial arrangement of atoms affording distinction between {{gli|stereoisomers}} which can be interconverted by rotations about formally {{gli|single bonds}}.}}

{{term|conjugated system}}{{anchor|conjugated systems}} {{defn|defn=A {{gli|molecule}} that contains {{gli|double bond|double}} or {{gli|triple bond|triple}} bonds separated by one {{gli|single bond}}; e.g. the compound buta-1,3-diene, with the chemical structure H2C=CH−CH=CH2, has conjugated double bonds. In such molecules, there is some {{gli|delocalized electron|delocalization}} of {{gli|electrons}} in the {{gli|pi bond|pi orbitals}} between the carbon atoms linked by the single bond.<ref name="Daintith"/>}}

{{term|constitutional isomer}} {{defn|See ''{{gli|structural isomer}}''.}}

{{term|constitutional unit}} {{defn|An atom or group of atoms (including {{gli|pendant}} atoms or groups, if any) comprising part of the structure of a {{gli|macromolecule}}, {{gli|oligomer}}, {{gli|polymer}}, {{gli|block}}, or {{gli|chain}}.<ref name="Gold Book"/>}}

{{term|cooling curve}} {{defn|A line graph representing the change between different {{gli|phases of matter}}, typically from a {{gli|gas}} to a {{gli|solid}} or a {{gli|liquid}} to a solid, as a function of time and temperature; e.g. showing how the temperature of a liquid substance changes over time as it {{gli|condenses}} below its {{gli|freezing point}}.}}

{{term|coordinate covalent bond}} {{defn|See ''{{gli|dipolar bond}}''.}}

{{term|coordination complex}}{{anchor|coordination complexes}} {{defn|A chemical {{gli|compound}} consisting of a central {{gli|atom}} or {{gli|ion}}, usually {{gli|metallic}} and known as the ''coordination center'', {{gli|bonded}} to a surrounding array of other groups of atoms, e.g. {{gli|molecules}} or ions, which are known as ''{{gli|ligands}}'' or ''complexing agents''. Many metal-containing compounds, especially those of the {{gli|transition metals}}, are coordination complexes. See also ''{{gli|complex}}''.}}

{{term|corrosion}}{{anchor|corrosive}} {{defn|An irreversible interfacial {{gli|chemical reaction}} of a material, especially a {{gli|metal}}, with its environment, which results in consumption of the material or {{gli|dissolution}} into the material of an external component of the environment.}}

{{term|coulomb (C)}}{{anchor|coulomb|coulombs}} {{defn|The {{gli|SI}} unit of {{gli|electric charge}}, defined as the charge transported by a constant {{gli|current}} of one ampere in one second.}}

{{term|counterion}} {{defn|The {{gli|ion}} that is the counterpart to an oppositely charged ion in a dissociated {{gli|ionic bond|ionic species}}; the {{gli|cation}} that pairs with a given {{gli|anion}}, or vice versa. For example, {{chem|Na|+}} is the counterion to {{chem|Cl|−}}, and vice versa, in solutions of sodium chloride (NaCl).}}

{{term|covalent bond}}{{anchor|covalent bonds|covalent bonding|covalently bonded|covalent|covalently}} {{ghat|Also '''molecular bond'''.}} {{defn|A {{gli|bond}} that involves the sharing of {{gli|electron pairs}} between {{gli|atoms}}. The stable balance of attractive and repulsive forces that occurs between atoms when they share electrons is known as ''covalent bonding''.}} thumb|right|350px|A diatomic hydrogen molecule, {{chem|H|2}} (right), is formed by a '''{{gli|covalent bond}}''' when two single hydrogen atoms share two electrons between them.

{{term|critical point}} {{defn|The end point of a {{gli|phase}} equilibrium curve or {{gli|pressure}}-{{gli|temperature}} curve at which conditions are such that {{gli|phase boundaries}} vanish and a substance's different phases, such as {{gli|liquid}} and {{gli|vapor}}, can coexist. The critical point is defined by the intersection of a critical temperature, ''T''c, and a critical pressure, ''p''c; above this temperature and pressure, all distinction between phases disappears and the substance becomes a {{gli|supercritical fluid}}.}}

{{term|crucible}} {{defn|A ceramic or metal dish or other vessel in which substances can be melted or otherwise subjected to very high temperatures.<ref name="Daintith"/>}}

{{term|crystal}}{{anchor|crystals|crystalline}} {{defn|A {{gli|solid}} whose constituent particles (such as atoms, ions, or molecules) are arranged in an orderly periodic microscopic structure, forming a {{gli|lattice}} with definite geometry that extends in all directions. Such materials are often described as ''crystalline''.}}

{{term|crystallization point}} {{defn|See ''{{gli|freezing point}}''.}}

{{term|crystallography}} {{defn|The branch of chemistry concerned with the study of {{gli|crystal|crystalline}} solids, including determining their structure and properties.}}

{{term|cuvette}}{{anchor|cuvettes}} {{defn|A type of small container used in {{gli|spectroscopy}} experiments, usually made of plastic, glass, or quartz and designed to hold a sample (typically a liquid) for measurement inside a {{gli|spectrometer}}. Cuvettes should be as clean and transparent as possible to minimize interference with the beams of light on which spectroscopic techniques rely.}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== D == {{glossary}} {{term|dalton (Da)}}{{anchor|daltons|unified atomic mass unit|unified atomic mass units}} {{ghat|Also '''unified atomic mass unit''' ('''u''').}} {{defn|A unit of {{gli|mass}} defined as {{frac|12}} of the mass of a free unexcited atom of carbon-12 at rest. It is approximately equal to the mass of one {{gli|nucleon}}.}}

{{term|Dalton's law of partial pressures}}{{anchor|Dalton's law}} {{defn|An empirical law which states that in a mixture of non-reacting {{gli|gases}}, the total {{gli|pressure}} exerted by all of the gases combined is equal to the sum of the partial pressures exerted by each gas individually.}}

{{term|dative bond}} {{defn|See ''{{gli|dipolar bond}}''.}}

{{term|debye (D)}}{{anchor|debye|debyes}} {{defn|A non-SI unit of measurement of {{gli|electric dipole moment}}, defined as {{10^|-18}} statcoulomb-centimetres. See also ''{{gli|electric dipole moment}}''.}}

{{term|deionization}}{{anchor|deionize|deionized}} {{defn|The removal of {{gli|ions}} from a solution by any method. In the case of water, this typically refers to mineral ions such as sodium, iron, and calcium.}}

{{term|deliquescence}} {{defn|A substance's affinity for {{gli|water}}, often characterized as its tendency to absorb moisture from the atmosphere to form {{gli|aqueous solutions}}. Most strongly deliquescent substances are {{gli|salts}}, such as calcium chloride and potassium carbonate.}}

{{term|delocalized electron}}{{anchor|delocalized electrons}} {{defn|Any {{gli|electron}} in a molecule, ion, or solid {{gli|metal}} that is not associated with an individual atom or {{gli|covalent bond}}. The term may refer to electrons involved in {{gli|resonance}} in {{gli|conjugated systems}} or {{gli|aromatic}} compounds; to free electrons which facilitate electrical conductivity; or to electrons within delocalized {{gli|molecular orbitals}} encompassing several adjacent atoms.}}

{{term|density}} {{defn|defn=An {{gli|intensive property}} of a substance defined as {{gli|mass}} per unit {{gli|volume}} and expressed by the equation ''d'' = ''m''/''V''.}}

{{term|denticity}} {{defn|The number of donor groups in a single {{gli|ligand}} that bind to a central atom in a {{gli|coordination complex}}.}}

{{term|depression of freezing point}} {{defn|See ''{{gli|freezing-point depression}}''.}}

{{term|desiccant}} {{ghat|Also '''drying agent'''.}} {{defn|A {{gli|hygroscopic}} substance used to induce or sustain a state of dryness or {{gli|desiccation}} (i.e. the absence of moisture) in its vicinity by abstracting water molecules from other substances. Desiccants come in many different forms and work by many different principles, ranging from simple {{gli|absorption}} to the chemical bonding of water molecules.}}

{{term|deuterium}} {{ghat|Also '''hydrogen-2''' or '''heavy hydrogen''', and symbolized '''{{chem|2|H}}''' or '''D'''.}} {{defn|One of two stable {{gli|isotopes}} of a {{gli|hydrogen}} atom, the {{gli|deuteron|nucleus of which}} contains one {{gli|proton}} and one {{gli|neutron}}. Deuterium is both heavier and much less abundant in nature than the other stable isotope, known as {{gli|protium}} ({{chem|1|H}}).}}

{{term|deuteron}} {{defn|The {{gli|nucleus}} of a {{gli|deuterium}} atom (an isotope of {{gli|hydrogen}}), containing one {{gli|proton}} and one {{gli|neutron}}.}}

{{term|Dewar flask}} {{defn|See ''{{gli|vacuum flask}}''.}}

{{term|dianion}}{{anchor|dianions}} {{defn|A compound or molecular entity bearing exactly two negative charges, which may be located on a single atom or on different atoms, or may be delocalized.<ref name="Gold Book"/>}}

{{term|diatomic}} {{defn|Composed of two atoms, of the same or different elements. Contrast ''{{gli|monatomic}}'' and ''{{gli|polyatomic}}''.}}

{{term|diatomic molecule}} {{defn|Any {{gli|molecule}} composed of only two {{gli|atoms}}, of the same or different {{gli|elements}}.}}

{{term|diffusion}}{{anchor|diffuse|diffuses|diffusing|diffused}} {{defn|The net movement of {{gli|atoms}} or {{gli|molecule|molecules}} from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in chemical potential of the diffusing species and depends on the random walk of particles; hence it results in mixing or mass transport without required directed bulk motion.}}

{{term|dilatant}} {{defn|A substance with the ability to increase in {{gli|volume}} when its shape is changed.<ref name="McGraw-Hill"/>}}

{{term|dimer}}{{anchor|dimers}} {{defn|An {{gli|oligomer}} consisting of two {{gli|monomers}} joined by chemical bonds that may variably be strong or weak, {{gli|covalent}} or {{gli|intermolecular force|intermolecular}}. A ''homodimer'' consists of two identical molecules; a ''heterodimer'' consists of two different molecules.}}

{{term|dipolar bond}}{{anchor|dipolar bonds|coordinate covalent bond|coordinate covalent bonds|coordinate bond|coordinate bonds|dative bond|dative bonds|semipolar bond|semipolar bonds}} {{ghat|Also '''coordinate covalent bond''', '''coordinate bond''', '''dative bond,''' and '''semipolar bond'''.}} {{defn|A type of {{gli|covalent bond}} formed by the {{gli|coordination}} of two or more electrically neutral {{gli|moieties}}, the combination of which results in a {{gli|polar compound|charge-separated molecule}} or {{gli|coordination complex}}, in which two {{gli|electrons}} deriving from the same atom are shared between the donor atom and an acceptor atom, creating an internal two-center {{gli|molecular dipole moment}}.<ref name="Gold Book"/>}}

{{term|dipole}}{{anchor|dipoles}} {{defn|The electric or magnetic separation of {{gli|electric charge}} into a pair of charges of equal magnitude but opposite sign, one positively charged and one negatively charged, separated by some typically small distance.}}

{{term|dipole moment}} {{defn|See ''{{gli|electric dipole moment}}'', ''{{gli|magnetic dipole moment}}'', ''{{gli|molecular dipole moment}}'', ''{{gli|bond dipole moment}}'', ''{{gli|electron electric dipole moment}}'', ''{{gli|electron magnetic dipole moment}}'', and ''{{gli|nuclear magnetic moment}}''.}}

{{term|dispersion}}{{anchor|disperse|disperses|dispersed}} {{defn|A system in which particles of one material are distributed within a continuous {{gli|phase}} of another material; the two phases may be in the same or different {{gli|states of matter}}. Dispersions of particles sufficiently large for sedimentation are called {{gli|suspensions}}, while those of smaller particles are called {{gli|colloids}} or {{gli|solutions}}.}}

{{term|dissociation}} {{defn|Any process by which a {{gli|polyatomic}} {{gli|molecule}} or molecular entity (e.g. an {{gli|ionic compound}} or {{gli|coordination complex}}), or an aggregate of molecular entities, separates or splits into two or more molecules, atoms, ions, radicals, or other constituents, usually in a {{gli|reversible}} manner. Examples include unimolecular {{gli|heterolysis}} and {{gli|homolysis}}, the {{gli|dissolution}} of {{gli|salts}}, and {{gli|acid dissociation constant|acid dissociation}}. Contrast ''{{gli|association}}''.}}

{{term|dissolution}}{{anchor|dissolve|dissolves|dissolving|dissolved}} {{ghat|Also '''solvation'''.}} {{defn|The interaction of a {{gli|solvent}} with the molecules or ions of a {{gli|solute}}, involving bond formation, {{gli|hydrogen bonding}}, and {{gli|van der Waals forces}}.}} thumb|right|350px|A sodium ion (Na+) forms a solvation complex with water molecules when '''{{gli|dissolved}}''' in an aqueous solution.

{{term|distillation}} {{defn|The process of separating the component substances of a {{gli|liquid}} {{gli|mixture}} by exploiting differences in the relative {{gli|volatility}} of the mixture's components through selective {{gli|boiling}} and subsequent {{gli|condensation}}. The apparatus used to distill a substance is called a ''still'', and the re-condensed substance yielded by the process is called the ''distillate''.}}

{{term|double bond}}{{anchor|double bonds|double-bonded}} {{defn|A {{gli|bond}} involving the {{gli|covalent}} sharing of two {{gli|electron pair|pairs of electrons}}.}}

{{term|double salt}} {{defn|no=1|A {{gli|salt}} composed of more than one different {{gli|cation}} or {{gli|anion}}, or which upon {{gli|hydrolysis}} forms two different cations and anions.}} {{defn|no=2|A salt that is a molecular combination of two other salts.<ref name="McGraw-Hill"/>}}

{{term|dropping point}} {{defn|The {{gli|temperature}} at which a {{gli|grease}} changes from a semi-{{gli|solid}} to a {{gli|liquid}} state under standardized conditions,<ref name="McGraw-Hill"/> i.e. the upper limit at which the grease retains its structure, though not necessarily the maximum temperature at which it can be used.}}

{{term|dry box}} {{defn|A chamber or container in which the interior is maintained at very low humidity, often by filling it with argon or with air lacking carbon dioxide, in order to provide an {{gli|inert}} atmosphere in which manipulation of very reactive chemicals or moisture-sensitive procedures can be carried out in the laboratory.<ref name="McGraw-Hill"/>}}

{{term|drying agent}} {{defn|See ''{{gli|desiccant}}''.}}

{{term|ductility}} {{ghat|Also '''malleability'''.}} {{defn|A measure of a material's ability to undergo significant plastic deformation before rupturing, typically expressed as percent elongation or percent area reduction from a tensile test and popularly characterized by the material's ability to be stretched into a wire.}}

{{term|dystectic mixture}} {{defn|A {{gli|mixture}} of two or more substances which has the highest {{gli|melting point}} of all possible mixtures of these substances.<ref name="McGraw-Hill"/> Contrast ''{{gli|eutectic mixture}}''.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== E == {{glossary}} {{term|earth metal}} {{defn|See ''{{gli|alkaline earth metal}}''.}}

{{term|ebullition}} {{defn|See ''{{gli|boiling}}''.}}

{{term|effective molecular diameter}} {{defn|The physical extent of the {{gli|electron cloud}} surrounding a {{gli|molecule}} of a particular gas, as calculated in any of several ways and usually expressed in {{gli|nanometre|nanometres}} or {{gli|angstrom|ångströms}}.<ref name="McGraw-Hill"/>}}

{{term|effervescence}} {{defn|The escape of {{gli|gas}} from an {{gli|aqueous}} {{gli|solution}} without the application of heat, and the bubbling, foaming, or fizzing that results; e.g. the release of carbon dioxide from carbonated water.}}

{{term|electric charge}} {{defn|A measured property ({{gli|coulomb|coulombs}}) that determines electromagnetic interaction.}}

{{term|electric dipole moment}} {{defn|A measure of the {{gli|dipole|separation}} of positive and negative {{gli|electric charge|electric charges}} within an electrical system, i.e. a measure of the system's overall electrical {{gli|polarity}}. The SI unit for measuring electric dipole moment is the {{gli|coulomb-metre}} (C⋅m), but the {{gli|debye}} (D), a non-SI unit, is also widely used in chemistry and atomic physics.}}

{{term|electride}} {{defn|An {{gli|ionic compound}} for which the {{gli|anion}} is an {{gli|electron}}.}}

{{term|electrochemical cell}}{{anchor|electrochemical cells}} {{defn|A device capable of either generating electrical energy from chemical reactions, in which case it is known as a galvanic or voltaic cell, or using electrical energy to cause chemical reactions, in which case it is known as an electrolytic cell. For example, a battery contains one or more galvanic cells, each of which consists of two {{gli|electrode|electrodes}} arranged such that an {{gli|redox|oxidation–reduction}} reaction produces an {{gli|electromotive force}}.}}

{{term|electrochemistry}} {{defn|A branch of {{gli|physical chemistry}} concerned with the relationship between electrical potential difference and identifiable chemical change, as understood through either the {{gli|chemical reaction|chemical reactions}} accompanying the passage of an electric current or the potential difference that results from a particular chemical reaction.}}

{{term|electrolyte}}{{anchor|electrolytes}} {{defn|A {{gli|solution}} that conducts a certain amount of electric current and can be split categorically into weak and strong electrolytes.}}

{{term|electromagnetic radiation}} {{defn|A type of wave that can go through vacuums as well as material and is classified as a self-propagating wave.}}

{{term|electromagnetism}} {{defn|Fields with an electric charge and electrical properties that change the way that particles move and interact.}}

{{term|electron}}{{anchor|electrons}} {{defn|A type of {{gli|subatomic particle}} with a net charge that is negative. Contrast ''{{gli|positron}}''.}}

{{term|electron capture}} {{defn|A type of nuclear transformation by which the {{gli|proton}}-rich {{gli|nucleus}} of an electrically neutral atom absorbs or 'captures' an {{gli|electron}} from one of its own inner shells, often those closest to the nucleus, which provokes a reaction that results in a nuclear proton changing into a {{gli|neutron}} accompanied by the simultaneous emission of an {{gli|electron neutrino}}.<ref name="Gold Book"/>}}

{{term|electron configuration}} {{defn|The distribution of the {{gli|electrons}} of an {{gli|atom}} or {{gli|molecule}} within {{gli|atomic orbital|atomic}} or {{gli|molecular orbitals}}. An extensive system of notation is used to concisely and uniquely display information about the electron configuration of each atomic species. Knowledge of the specific arrangements of electrons in different atoms is useful for understanding {{gli|chemical bonds}} and the organization of the {{gli|periodic table of the elements}}.}}

{{term|term=electron electric dipole moment|content=electron electric dipole moment ({{math|de}})}} {{defn|An intrinsic property of an {{gli|electron}} such that its potential energy is linearly related to the strength of its electric field; a measure of the distribution of an electron's negative charge within the electric field it creates. See also ''{{gli|electric dipole moment}}''.}}

{{term|electron magnetic dipole moment}} {{ghat|Also '''electron magnetic moment'''.}} {{defn|The {{gli|magnetic moment}} of an {{gli|electron}}, caused by the intrinsic properties of its spin and {{gli|electric charge}}, equal to approximately −9.284764{{x10^|-24}} {{gli|joules}} per tesla.}}

{{term|electron pair}}{{anchor|electron pairs}} {{defn|Two {{gli|electrons}} which occupy the same {{gli|molecular orbital}} but have opposite spins. Electron pairs form {{gli|chemical bonds}} or occur as {{gli|lone pairs}} of {{gli|valence electrons}}; it is also possible for electrons to occur individually as {{gli|unpaired electrons}}.}}

{{term|electron shell}}{{anchor|electron shells}} {{defn|An {{gli|atomic orbital|orbital}} around the {{gli|nucleus}} of an {{gli|atom}} which contains a fixed number of {{gli|electrons}} (usually two or eight).}}

{{term|electronegativity (''χ'')}}{{anchor|electronegativity|electronegative}} {{defn|A chemical property that describes the tendency of an {{gli|atom}} to attract a shared {{gli|electron pair|pair}} of {{gli|electrons}} (or {{gli|electron density}}) towards itself. An atom's electronegativity is affected both by its {{gli|effective nuclear charge|nuclear charge}} (which is proportional to the {{gli|atomic number|number of protons}} in its {{gli|nucleus}}) and the number and location of the electrons present in its {{gli|electron shell|atomic shells}} (which influences the distance of the nucleus from the {{gli|valence electrons}}). The higher an atom or {{gli|substituent}}'s electronegativity, the more it attracts electrons towards itself. As it is usually calculated, electronegativity is not a property of an atom alone but rather of an atom within a {{gli|molecule}}; it therefore varies with an element's chemical environment, though it is generally considered a {{gli|transferability|transferable property}}.}}

{{term|electrophile}}{{anchor|electrophiles|electrophilic}} {{defn|Any atom or molecule which can accept an {{gli|electron pair}}. Most electrophiles carry a net {{gli|electric charge|positive charge}}, include an atom carrying a partial positive charge, or include a neutral atom that does not have a complete {{gli|octet rule|octet}} of electrons, and therefore they attract electron-rich regions of other species; an electrophile with vacant orbitals can accept an electron pair donated by a {{gli|nucleophile}}, creating a chemical bond between the two species. Because they accept electrons, electrophiles are {{gli|Lewis acids}} by definition.}}

{{term|element}}{{anchor|elements|chemical element|chemical elements|elemental}} {{defn|A species of {{gli|atoms}} having the same number of {{gli|protons}} in their {{gli|nucleus|atomic nuclei}} and hence the same {{gli|atomic number}}. Chemical elements constitute all of the ordinary {{gli|matter}} in the universe; 118 elements have been identified and are organized by their various chemical properties in the {{gli|periodic table of the elements}}.}}

{{term|elementary reaction}} {{defn|Any {{gli|chemical reaction}} in which one or more {{gli|chemical species}} react directly to form {{gli|products}} in a single {{gli|reaction step}} and with a single {{gli|transition state}}, i.e. without any {{gli|reactive intermediate|intermediates}}. Contrast ''{{gli|stepwise reaction}}''.}}

{{term|elution}} {{defn|The process of extracting one material from another by washing with a {{gli|solvent}}. Elution works by running a solution containing an {{gli|analyte}} past an {{gli|adsorbent}} matrix designed to selectively bind the analyte molecules, and subsequently washing the adsorbent/analyte complex with a solvent, known as an ''eluent''. The solvent molecules displace the analyte by binding to the adsorbent in its place, allowing the analyte, now part of the ''eluate'', to be carried out of the complex and into a collector for analysis.}}

{{term|empirical formula}} {{defn|The simplest whole-number ratio of the {{gli|atoms}} of each {{gli|element}} present in a {{gli|chemical compound}}.}}

{{term|emulsion}} {{defn|A type of {{gli|colloid}} in which small particles of one {{gli|liquid}} are {{gli|dispersed}} in another liquid; e.g. a dispersion of water in an oil, or of an oil in water. Emulsions are often stabilized by the addition of a substance, known as an ''emulsifier'', that has both lyophilic and lyophobic parts in its molecules.<ref name="Daintith"/>}}

{{term|end-group}}{{anchor|end-groups}} {{defn|A {{gli|constitutional unit}} that occupies a terminal position within or is at an extremity of a {{gli|macromolecule}} or {{gli|polymer}}, and thus by definition is connected to only one other constitutional unit of the molecule.<ref name="Gold Book"/>}}

{{term|energy}} {{defn|A system's ability to do {{gli|work}}.}}

{{term|enplethy}} {{defn|See ''{{gli|amount of substance}}''.}}

{{term|enthalpy}} {{defn|A measure of the total internal energy of a thermodynamic system, usually symbolized by ''H''.}}

{{term|entropy}} {{defn|The amount of energy that is not available for {{gli|work}} in a closed thermodynamic system, usually symbolized by ''S''.}}

{{term|enzyme}} {{defn|A biological protein {{gli|catalyst}} that speeds up a chemical reaction.}}

{{term|Eppendorf tube}} {{defn|A generalized and trademarked name used to refer to a {{gli|microcentrifuge tube}}.}}

{{term|equilibrium}} {{defn|The condition of a system in which all competing influences are balanced. Chemical equilibrium is the state in which the concentrations of the {{gli|reactant|reactants}} and {{gli|product|products}} in a {{gli|chemical reaction|reacting}} system have stopped changing in time.}}

{{term|equimolar}} {{defn|Having an equal number of {{gli|mole}}s, or {{gli|solution}}s of equal {{gli|molar concentration}}.}}

{{term|ester}}{{anchor|esters}} {{defn|A class of {{gli|organic}} and {{gli|inorganic}} compounds derived from the reaction of an {{gli|acid}} with an {{gli|alcohol}}, in which at least one {{gli|hydroxyl}} group (–OH) is replaced by an {{gli|alkoxy}} group (–O–). Esters have the general formula RCO2R′, where R and R' represent any {{gli|alkyl}} or {{gli|aryl}} group.}} thumb|right|350px|The skeletal formula for a generic '''{{gli|ester}}''', with R and R′ denoting variable carbon-containing substituent groups

{{term|ether}}{{anchor|ethers}} {{defn|A class of {{gli|organic compounds}} and a {{gli|functional group}} containing an oxygen atom connected to two {{gli|alkyl}} or {{gli|aryl}} groups, which may be the same or different. Ethers have the general formula R–O–R′, where R and R′ represent the alkyl or aryl groups.}} thumb|right|350px|The skeletal formula for a generic '''{{gli|ether}}''', with R and R′ denoting variable carbon-containing substituent groups

{{term|ethyl}} {{defn|The {{gli|alkyl}} {{gli|functional group}} derived from ethane, consisting of two carbon atoms covalently bonded to each other and fully saturated with bonds to hydrogen atoms, with the chemical formula –{{chem|CH|2|CH|3}}. It is a common {{gli|substituent}} in numerous organic compounds, though it may also exist independently as an ion or radical. In IUPAC nomenclature, the presence of an ethyl substituent may be indicated with the prefix ''ethyl'' in the name of the compound, or with the abbreviation ''Et'' in chemical formulae; e.g. ethyl alcohol (ethanol), which is often written with the formula {{chem|CH|3|CH|2|OH}} or {{chem|Et|OH}}.}}

{{term|eutectic mixture}} {{defn|A {{gli|solid}} {{gli|solution}} consisting of two or more substances which collectively have the lowest {{gli|melting point}} of any possible mixture of these components.<ref name="Daintith"/>}}

{{term|extensive property}} {{defn|A physical quantity whose value is proportional to the size of the system it describes or to the quantity of {{gli|matter}} in the system. Examples include {{gli|mass}}, {{gli|volume}}, {{gli|enthalpy}}, and {{gli|entropy}}. Contrast ''{{gli|intensive property}}''.}}

{{term|extraction}} {{defn|no=1|A separation process in which a component is separated from its {{gli|mixture}} by selective {{gli|solubility}}.<ref name="Daintith"/> See also ''{{gli|partition}}''.}} {{defn|no=2|The separation of a component {{gli|analyte}} from a {{gli|matrix}}.}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== F == {{glossary}} {{term|family}} {{defn|See ''{{gli|group}}''.}}

{{term|Faraday constant (''F'')}} {{defn|defn=A unit of {{gli|electric charge}} widely used in {{gli|electrochemistry}} equal to the negative of the molar charge (electric charge per mole) of {{gli|electrons}}. It is equal to approximately 96,500 {{gli|coulomb|coulombs}} per {{gli|mole}} (''F'' = {{val|96485.33212|end=...|u=C/mol}}).}}

{{term|Faraday's laws of electrolysis}} {{defn|A set of two laws pertaining to electrolysis which hold that: a) the mass of a substance altered at an electrode during electrolysis is directly proportional to the quantity of electricity transferred at that electrode; and b) the mass of an elemental material altered at an electrode is directly proportional to the element's equivalent weight.}}

{{term|filtration}} {{defn|Any physical, biological, or chemical operation that separates large particles (often {{gli|solid}} matter) from smaller particles (often a fluid) by passing the {{gli|mixture}} through a complex lattice structure through which only particles of a sufficiently small size can pass, called a ''filter''. The fluid and small particles which successfully pass through the filter are called the ''filtrate''.}}

{{term|fire point}} {{defn|The lowest {{gli|temperature}} at which the {{gli|vapor|vapors}} above a {{gli|volatile}} material will continue to {{gli|combustion|burn}} for at least five seconds after ignition by an open flame of standard dimension.<ref>{{Cite book|last=Steven A.|first=Treese|title=Handbook of Petroleum Processing|last2=Peter R.|first2=Pujado|last3=David S. J.|first3=Jones|publisher=Springer|year=2015|isbn=978-3-319-14528-0|edition=2|pages=1736}}</ref> The fire point should not be confused with the {{gli|flash point}}, a slightly lower temperature at which a substance will ignite briefly but at which vapor is not produced at a rate sufficient for sustained combustion.}}

{{term|flash point}} {{defn|The lowest {{gli|temperature}} at which the {{gli|vapor|vapors}} above a {{gli|volatile}} material will {{gli|combustion|ignite}} if given an ignition source. At the flash point, the application of an open flame causes only a momentary "flash" rather than sustained combustion, for which the ambient temperature is still too low. The flash point should not be confused with the {{gli|fire point}}, which occurs at a slightly higher temperature, nor with the {{gli|autoignition temperature|kindling point}}, which is higher still.}}

{{term|flask}}{{anchor|flasks}} {{defn|A vessel or container, most commonly a type of glassware, widely used in laboratories for a variety of purposes, such as preparing, holding, containing, collecting, and volumetrically measuring chemicals, samples, or solutions, or as a chamber in which a {{gli|chemical reaction}} occurs. Flasks come in a number of shapes and sizes but are typically characterized by a relatively wide lower body which tapers into one or more narrower tubular sections with an opening at the top.}}

{{term|flocculation}} {{defn|The process by which the dispersed particles in a {{gli|colloid}} come out of {{gli|suspension}} to aggregate into larger clumps known as ''floc'' or ''flake'', either spontaneously or due to the addition of a clarifying agent. The term is often used to refer to a reversible aggregation in which the forces holding the particles together are weak and the colloid can be re-dispersed by agitation.<ref name="Daintith"/>}}

{{term|Florence flask}} {{defn|See ''{{gli|boiling flask}}''.}}

{{term|formal charge (FC)}} {{defn|The {{gli|electric charge}} assigned to an {{gli|atom}} in a {{gli|molecule}}, assuming that all {{gli|electrons}} in all {{gli|chemical bond|bonds}} are shared equally between atoms, regardless of each atom's relative {{gli|electronegativity}}. The formal charge of any atom that is part of a molecule can be calculated by the equation <math>FC = V - N - \frac{B}{2}\ </math>, where <math>V</math> is the number of {{gli|valence electron|valence electrons}} of the neutral atom in its {{gli|ground state}}; <math>N</math> is the number of valence electrons of the atom which are not participating in bonds in the molecule; and <math>B</math> is the number of electrons shared in bonds with other atoms in the molecule.}}

{{term|formula weight (FW)}} {{defn|A synonym for {{gli|molar mass}} and {{gli|molecular weight}}, frequently used for non-molecular compounds such as {{gli|ionic bond|ionic salts}}.}}

{{term|fractional distillation}} {{defn|The {{gli|fractionation}} of a {{gli|mixture}} of {{gli|liquid|liquids}} into its component parts, or {{gli|fraction|fractions}}, by the process of {{gli|distillation}}, typically by using a long vertical column attached to the distillation vessel and filled with glass beads. The mixture is heated to a temperature at which one or more of the component compounds will {{gli|vaporization|vaporize}}; the {{gli|vapor}} rises up the column until it {{gli|condensation|condenses}} and runs back into the vessel, creating a temperature and {{gli|volatility}} gradient and permitting various fractions to be drawn off at different points along the length of the column.<ref name="Daintith"/> Common in industrial chemistry, the technique is sensitive enough to separate compounds which have {{gli|boiling point|boiling points}} that differ by less than {{convert|25|C-change|F-change}} from each other at standard pressure.}} thumb|right|350px|A diagram of a laboratory apparatus designed for '''{{gli|fractional distillation}}'''

{{term|fractionation}} {{defn|A separation process in which a particular quantity of a {{gli|mixture}} is divided during a {{gli|phase transition}} into a number of smaller quantities, known as {{gli|fraction|fractions}}, for which the chemical composition varies according to a gradient. Fractionation exploits subtle differences in some specific property (e.g. {{gli|mass}}, {{gli|boiling point}}, {{gli|solubility}}, etc.) between the mixture's component {{gli|compound|compounds}}, making it possible to isolate more than two components of a mixture at the same time. There are many varieties of fractionation employed in many branches of science and technology.}}

{{term|free radical}} {{defn|See ''{{gli|radical}}''.}}

{{term|freeze-drying}} {{defn|See ''{{gli|lyophilization}}''.}}

{{term|freezing}} {{defn|The {{gli|phase transition}} of a substance from a {{gli|liquid}} to a {{gli|solid}}.}}

{{term|freezing point}} {{ghat|Also '''crystallization point'''.}} {{defn|The {{gli|temperature}} at which a substance changes {{gli|state of matter|state}} from a {{gli|liquid}} to a {{gli|solid}}. Because {{gli|freezing}} is the reverse of {{gli|melting}}, the freezing point of a substance is identical to its {{gli|melting point}}, but by convention only the melting point is referred to as a characteristic property of a substance.}}

{{term|frequency}} {{defn|defn=A measurement of the number of cycles of a given process per unit of time. The {{gli|SI}} unit for measuring frequency is the hertz (Hz), with 1 Hz = 1 cycle per second.}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== G == {{glossary}} {{term|galvanic cell}}{{anchor|galvanic cells}} {{defn|A type of {{gli|battery}} made up of electrochemicals with two different metals connected by a {{gli|salt bridge}}.}}

{{term|gas}}{{anchor|gases|gaseous}} {{defn|One of the four fundamental {{gli|states of matter}}, characterized by high-energy particles which fill their container but have no definite shape or volume.}}

{{term|gas chromatography}} {{defn|A type of {{gli|chromatography}} commonly used in {{gli|analytical chemistry}} to isolate and analyze chemical compounds that can be {{gli|evaporation|vaporized}} without {{gli|chemical decomposition|decomposition}}. Gas chromatography is often used to test the purity of substances, to identify unknown substances, and to measure the relative amounts of the different components of {{gli|mixture|mixtures}}.}}

{{term|gauche}} {{defn|In {{gli|alkane}} {{gli|stereochemistry}}, a structural {{gli|conformation}} involving a {{gli|torsion angle}} of {{+-}}60°, or a {{gli|synclinal}} alignment of functional groups attached to adjacent atoms.<ref name="Gold Book"/>}}

{{term|Gay-Lussac's law}} {{defn|A chemical law used for each of the two relationships derived by French chemist Joseph Louis Gay-Lussac and which concern the properties of gases, though the name is more usually applied to his law of combining volumes.}}

{{term|geochemistry}} {{defn|The study of the chemistry and chemical composition of the Earth and geological processes.}}

{{term|Gibbs energy}} {{defn|A value that indicates the spontaneity of a reaction. Usually symbolized as ''G''.}}

{{term|glycol}} {{defn|Any of a class of {{gli|aliphatic}} {{gli|diol|dihydric alcohols}} in which the two {{gli|hydroxy}} groups are bonded to two different carbon atoms, which are usually but not necessarily adjacent to each other; e.g. ethylene glycol ({{chem|HO|CH|2|CH|2|OH}}).<ref name="Gold Book"/>}}

{{term|gram-atom}} {{defn|A former term for a {{gli|mole}}.}}

{{term|ground glass joint}} {{defn|An apparatus designed to quickly and easily fit two pieces of leak-tight glassware together, featuring ground glass surfaces and typically a custom-made conical taper.}}

{{term|ground state}} {{anchor|vacuum state}} {{defn|The lowest possible energy state for a given quantum mechanical system, at which the {{gli|Gibbs energy}} is actually or theoretically minimized. Whatever energy remains in the system in its ground state is called the {{gli|zero-point energy}}.<ref name="Gold Book"/> Contrast ''{{gli|excited state}}''.}}

{{term|group}}{{anchor|groups|family|families}} {{ghat|Also '''family'''.}} {{defn|A vertical column of the {{gli|periodic table|periodic table of the elements}} and the elements that share it. Contrast ''{{gli|period}}''.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== H == {{glossary}} {{term|hadron}} {{defn|A subatomic particle of a type including the baryons and mesons that can take part in the strong interaction.}}

{{term|halogen}}{{anchor|halogens}} {{defn|Any of the five {{gli|non-metal|non-metallic}} {{gli|elements}} of {{gli|group|Group 17}} of the {{gli|periodic table}}: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).}}

{{term|hard acid}} {{defn|A {{gli|Lewis acid}} with an electron-accepting centre that is only weakly {{gli|polarizable}}. Hard acid species also tend to have high charge states and relatively small atomic nuclei, in contrast to {{gli|soft acids}}.<ref name="Gold Book"/>}}

{{term|hard water}} {{defn|{{gli|water|Water}} that has very high {{gli|mineral}} content, generally formed when water {{gli|percolation|percolates}} through deposits rich in calcium, magnesium, and certain other metal {{gli|cation|cations}}.}}

{{term|heat}} {{defn|Energy transferred from one system to another by thermal interaction.}}

{{term|heat of fusion}} {{defn|See ''{{gli|enthalpy of fusion}}''.}}

{{term|heat of vaporization}} {{defn|See ''{{gli|enthalpy of vaporization}}''.}}

{{term|Hess' law of constant heat summation}} {{ghat|Also simply called '''Hess' law'''.}} {{defn|A law of {{gli|physical chemistry}} which states that the total {{gli|enthalpy}} change during the course of a chemical reaction is the same whether the reaction is completed in one step or in multiple steps.}}

{{term|hydrate}} {{defn|Any substance that contains water or its constituent elements, or any {{gli|compound}} formed by the addition of water or its elements to another molecule.}}

{{term|hydrogen bond}} {{defn|A form of electrostatic interaction between an {{gli|electronegativity|electronegative}} {{gli|atom}} and a {{gli|hydrogen}} atom bound to a second electronegative atom. Hydrogen bonding is unique because the small size of the hydrogen atoms permits proximity of the interacting {{gli|electrical charge|electrical charges}}, and may occur as an {{gli|intermolecular force|intermolecular}} or {{gli|intramolecular force|intramolecular}} force.}}

{{term|hydrogenation}} {{defn|Any chemical reaction between molecular {{gli|hydrogen}} ({{chem|H|2}}) and another chemical species, typically resulting in the {{gli|reduction}} or {{gli|saturation}} of the other species by the addition of one or more pairs of hydrogen atoms to a compound or element. The presence of a {{gli|catalyst}} is usually required for hydrogenation reactions to occur; non-catalytic hydrogenation takes place only at extreme temperatures.}}

{{term|hydrolysis}}{{anchor|hydrolytic}} {{defn|The cleavage of a {{gli|bond|chemical bond}} by the addition of {{gli|water}}.}}

{{term|term=hydron|content=hydron ({{chem|H|+}})}}{{anchor|hydron|hydrons}} {{ghat|Informally synonymous with '''proton'''.}} {{defn|The {{gli|cationic}} form of atomic {{gli|hydrogen}}; i.e. a positively charged hydrogen {{gli|nucleus}} of any {{gli|isotopic}} composition. Thus the term can refer to a {{gli|proton}} ({{chem|1|1|H|+}}), {{gli|deuteron}} ({{chem|1|2|H|+}}), or {{gli|triton}} ({{chem|1|3|H|+}}).}}

{{term|hydrous}} {{defn|Having or containing {{gli|water}} molecules, referring especially to {{gli|water of crystallization|water of hydration}}. Contrast ''{{gli|anhydrous}}''.}}

{{term|hydroxide}} {{defn|A {{gli|diatomic}} {{gli|anion}} consisting of a hydrogen atom covalently bonded to an oxygen atom, having an overall negative charge, with the chemical formula {{chem|OH|-}}; or any member of a class of organic and inorganic compounds containing a {{gli|hydroxy group}}, e.g. sodium hydroxide ({{chem|NaOH}}).<ref name="McGraw-Hill"/>}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== I == {{glossary}} {{term|ideal gas}}{{anchor|ideal gases}} {{defn|A hypothetical {{gli|gas}} composed of many randomly moving point particles that do not participate in any interparticle interactions, thereby making it mathematically convenient to describe and predict their behavior as state variables change. The ideal gas concept is useful because it obeys the {{gli|ideal gas law}} and can be analyzed within the framework of statistical mechanics.}}

{{term|ideal gas constant}} {{ghat|Also '''universal gas constant'''.}} {{defn|The proportionality constant in the {{gli|ideal gas law}}, defined as 0.08206 {{gli|liter|L}}·{{gli|atmosphere|atm}}/({{gli|kelvin|K}}·{{gli|mole|mol}}).}}

{{term|ideal gas law}} {{ghat|Also '''general gas equation'''.}} {{defn|defn=The {{gli|equation of state}} of a hypothetical {{gli|ideal gas}}, which states that the {{gli|volume}} of such a {{gli|gas}} is proportional to the {{gli|amount of substance|amount}} of gas and its {{gli|kelvin|Kelvin}} {{gli|temperature}}, and inversely proportional to its {{gli|pressure}}. The ideal gas law combines {{gli|Boyle's law}}, {{gli|Charles's law}}, {{gli|Gay-Lussac's law}}, and {{gli|Avogadro's law}} into a single equation, conventionally formulated as <math>PV = nRT</math>, where <math>R</math> is the {{gli|ideal gas constant}}. The relationships between the state variables described in this equation are a good approximation of the behavior of many gases under a wide range of conditions, though there are some limitations.}}

{{term|ideal solution}}{{anchor|ideal solutions}} {{defn|A {{gli|solution}} for which the {{gli|gas}} phase exhibits thermodynamic properties analogous to those of a mixture of {{gli|ideal gases}}.}}

{{term|indicator}} {{defn|A special compound added to a {{gli|solution}} that changes color depending on the {{gli|acidity}} of the solution. Different indicators have different colors and are effective within different {{gli|pH}} ranges.}}

{{term|induced radioactivity}} {{defn|{{gli|radioactivity|Radioactivity}} caused by bombarding a {{gli|stable isotope}} with elementary particles, forming an unstable, radioactive isotope.}}

{{term|inert}} {{defn|(of a chemical species) Stable and chemically unreactive;<ref name="Gold Book"/> or thermodynamically {{gli|lability|non-labile}}, decomposing at a slow or negligible rate. Examples of inert species include the {{gli|noble gases}}, which are stable in their naturally occurring forms because their outermost {{gli|electron shells}} are filled with as many electrons as possible, making them broadly resistant to the loss or gain of electrons.}}

{{term|inorganic compound}}{{anchor|inorganic compounds|inorganic}} {{defn|Any {{gli|chemical compound}} that does not contain {{gli|carbon}}, though there are exceptions. Contrast ''{{gli|organic compound}}''.}}

{{term|inorganic chemistry}} {{defn|The branch of chemistry concerning the chemical properties and reactions of {{gli|inorganic compound|inorganic compounds}}. Contrast ''{{gli|organic chemistry}}''.}}

{{term|insolubility}}{{anchor|insoluble}} {{defn|The inability of a substance (the {{gli|solute}}) to form a {{gli|solution}} by being dissolved in another substance (the {{gli|solvent}}); the opposite of {{gli|solubility}}.}}

{{term|inspissation}} {{defn|The process of thickening a {{gli|liquid}} by any method of {{gli|dehydration}}, especially {{gli|evaporation}}.<ref name="McGraw-Hill"/>}}

{{term|insulator}}{{anchor|insulators|insulating|insulated}} {{defn|Any material that resists the flow of an {{gli|electric current}}. Contrast ''{{gli|conductor}}''.}}

{{term|intensive property}} {{defn|A physical quantity whose value does not depend on the size of the system or the quantity of {{gli|matter}} for which it is measured. Examples include {{gli|density}}, {{gli|temperature}}, and {{gli|pressure}}. Contrast ''{{gli|extensive property}}''.}}

{{term|interface}} {{defn|The boundary between two spatial regions occupied by different {{gli|matter}}, especially by matter in different {{gli|phases}} or physical {{gli|states}}. See also ''{{gli|surface}}'' and ''{{gli|phase boundary}}''.}}

{{term|intermediate}} {{defn|See ''{{gli|reactive intermediate}}''.}}

{{term|intermetallic}} {{defn|A type of {{gli|alloy}} that forms an ordered solid-state compound between two or more {{gli|metallic}} elements. Intermetallics are generally hard and brittle, and have useful mechanical properties at high temperatures.}}

{{term|intermolecular force}}{{anchor|intermolecular forces}} {{defn|Any force that mediates interaction between {{gli|molecules}}, e.g. {{gli|electromagnetic}} forces of attraction or repulsion, {{gli|hydrogen bonding}}, and the {{gli|van der Waals force}}, all of which act between the atoms of one molecule and the atoms or ions of nearby molecules. Intermolecular forces are weak compared to {{gli|intramolecular forces}} such as {{gli|covalent bonds}}, which hold individual molecules together.}}

{{term|International Union of Pure and Applied Chemistry (IUPAC)}}{{anchor|International Union of Pure and Applied Chemistry|IUPAC}} {{defn|An international federation of chemists that is recognized as the world authority in developing standards for {{gli|chemical nomenclature}} and other methodologies in chemistry.}}

{{term|interstitial compound}} {{defn|A {{gli|compound}} composed of a {{gli|transition metal}} bonded to either hydrogen, boron, carbon, or nitrogen, whose {{gli|crystal}} structure consists of closely packed metal ions with the {{gli|non-metal}} atoms located in the interstices.<ref name="McGraw-Hill"/>}}

{{term|ion}}{{anchor|ions}} {{defn|A {{gli|molecule}} that has gained or lost one or more {{gli|electrons}} from its neutral state and therefore possesses a negative or positive {{gli|electric charge}}.}}

{{term|ionic bond}}{{anchor|ionic bonds|ionic}} {{defn|An electrostatic attraction between oppositely charged {{gli|ions}}.}} [[File:NaF.gif|thumb|right|350px|An '''{{gli|ionic bond}}''' between a sodium atom (Na) and a fluorine atom (F). The sodium atom loses its sole {{gli|valence electron}} (leaving the atom with a positive {{gli|electrical charge}}), and the fluorine atom gains this same electron via an {{gli|exothermic process}} (giving the atom a negative electrical charge). The oppositely charged {{gli|ions}} are then attracted to each other to form a new compound called sodium fluoride.]]

{{term|ionic strength}} {{defn|A measure of the {{gli|concentration}} of {{gli|ions}} in a {{gli|solution}}, usually expressed in terms of {{gli|molarity}} (mol/L solution) or {{gli|molality}} (mol/kg solvent).<ref>{{cite journal|doi=10.1021/ed078p1691|title=The definition and unit of ionic strength|journal=Journal of Chemical Education|volume=78|issue=12|pages=1691|year=2001|last1=Solomon|first1=Theodros|bibcode=2001JChEd..78.1691S}}</ref>}}

{{term|ionization}}{{anchor|ionize|ionizes|ionizing|ionized}} {{defn|The breaking up of a chemical {{gli|compound}} into separate {{gli|ions}}.}}

{{term|isoelectronicity}}{{anchor|isoelectronic}} {{defn|The phenomenon of two or more {{gli|chemical species}} ({{gli|atoms}}, {{gli|molecules}}, {{gli|ions}}, etc.) being composed of different {{gli|elements}} but having the same number of {{gli|valence electron|valence}} {{gli|electrons}} and the same structural arrangement (i.e. the same number of atoms with the same connectivity). Isoelectronic species typically show useful consistency and predictability in their chemical properties.}}

{{term|isomers}}{{anchor|isomer|isomeric}} {{defn|{{gli|ion|Ions}} or {{gli|molecules}} with identical {{gli|chemical formulas}} but distinct structures or spatial arrangements. Isomers do not necessarily share similar properties. The two main types of isomers are {{gli|structural isomers}} and {{gli|stereoisomers}}.}}

{{term|isotope}}{{anchor|isotopes|isotopic}} {{defn|A variant of a particular {{gli|chemical element}} which differs in the number of {{gli|neutrons}} present in the {{gli|nucleus}}. All isotopes of a given element have the same number of {{gli|protons}} in each {{gli|atom}}.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== J == {{glossary}} {{term|joule (J)}}{{anchor|joule|joules}} {{defn|The {{gli|SI}} unit of {{gli|energy}} (symbol: J). One joule is defined as one newton-metre.}} {{glossary end}}

== K == {{glossary}} {{term|kelvin (K)}}{{anchor|kelvin|kelvins}} {{defn|The {{gli|SI}} unit of {{gli|temperature}} (symbol: K). The Kelvin scale is an absolute thermodynamic temperature scale that uses {{gli|absolute zero}} as its null point.}}

{{term|keto acid}} {{ghat|Also '''ketoacid'''.}} {{defn|Any organic compound that can be classified as both a {{gli|ketone}} and a {{gli|carboxylic acid}}, by virtue of containing a {{gli|keto}} group and a {{gli|carboxyl}} group.<ref name="McGraw-Hill"/>}}

{{term|ketone}}{{anchor|ketones}} {{defn|defn=A class of {{gli|organic compound|organic compounds}} and a {{gli|functional group}} composed of a {{gli|carbonyl}} group between two {{gli|carbon}} atoms. Ketones have the general formula R2C=O, where R can be any carbon-containing {{gli|substituent}}.}} thumb|right|350px|The skeletal formula for a generic '''{{gli|ketone}}''', with R and R′ denoting variable carbon-containing substituent groups

{{term|kindling point}} {{defn|See ''{{gli|autoignition temperature}}''.}}

{{term|kinetics}} {{defn|A subfield of chemistry specializing in the study of {{gli|reaction rates}}.}}

{{term|kinetic energy}} {{defn|The {{gli|energy}} of an object due to its motion.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== L == {{glossary}} {{term|lability}} {{defn|}}

{{term|lanthanides}}{{anchor|lanthanide}} {{ghat|Also '''lanthanoids'''.}} {{defn|The {{gli|period|periodic}} series of {{gli|metal|metallic}} elements with atomic numbers 57 through 71, from lanthanum through lutetium.}}

{{term|lattice}}{{anchor|lattices}} {{defn|The unique geometric arrangement of atoms or molecules in a {{gli|crystal|crystalline}} liquid or solid.}}

{{term|lattice energy}} {{defn|The energy released upon the formation of one {{gli|mole}} of a crystalline {{gli|ionic compound}} from its constituent ions, which are assumed to exist initially in the gaseous state. Lattice energy can be viewed as a measure of the cohesive forces that bind ionic solids; it is therefore directly related to many other physical properties of the solid, including {{gli|solubility}}, {{gli|hardness}}, and {{gli|volatility}}.}}

{{term|leveling effect}} {{defn|The effect of a {{gli|solvent}} on the chemical properties of {{gli|acids}} or {{gli|bases}} which are dissolved in the solvent. The strength of a strong acid is limited or "leveled" by the basicity of the solvent, and likewise the strength of a strong base is limited by the acidity of the solvent, such that the effective {{gli|pH}} of the solution is higher or lower than might be suggested by the acid's or base's {{gli|acid dissociation constant|dissociation constant}}.}}

{{term|ligand}}{{anchor|ligands}} {{defn|An {{gli|ion}}, {{gli|functional group}}, or other {{gli|molecule}} that binds to a central {{gli|metal}} atom to form a {{gli|coordination complex}}. Such bonding can range from {{gli|covalent}} to {{gli|ionic}}, but generally involves formal donation of one or more of the ligand's {{gli|electron pairs}} to the metal.}}

{{term|light}} {{ghat|Also referred to as '''visible light'''.}} {{defn|The portion of the {{gli|electromagnetic spectrum}} which is visible to the unaided human eye.}}

{{term|liquefaction}} {{defn|Any process that generates a {{gli|liquid}} from a {{gli|solid}} or a {{gli|gas}}, or that generates a non-liquid phase that behaves as a {{gli|fluid}}.}}

{{term|liquefaction point}} {{defn|See ''{{gli|melting point}}''.}}

{{term|liquid}}{{anchor|liquids}} {{defn|One of the four fundamental {{gli|states of matter}}, characterized by nearly incompressible fluid particles that retain a definite volume but no fixed shape.}}

{{term|London dispersion forces}} {{defn|A type of weak {{gli|intermolecular force}}.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== M == {{glossary}} {{term|macromolecule}}{{anchor|macromolecules|macromolecular}} {{defn|A very large {{gli|molecule}} comprising many {{gli|atoms}} and {{gli|bonds}}, or any {{gli|molecule}} with a high {{gli|relative molecular mass}}, especially one whose structure is formed by the multiple repetition of discrete subunits derived, actually or conceptually, from molecules with low relative molecular mass (e.g. {{gli|monomers}}, {{gli|substituents}}, and {{gli|functional groups}}). The term is often used interchangeably with {{gli|polymer}}.<ref name="Gold Book"/>}}

{{term|malleability}} {{defn|See ''{{gli|ductility}}''.}}

{{term|manometer}} {{defn|An instrument used to measure {{gli|pressure}} invented by Evangelista Torricelli in 1643.}}

{{term|marine biochemistry}} {{defn|study of the chemical processes and interactions within and between marine organisms and their marine environment.}}

{{term|masking agent}} {{defn|A {{gli|reagent}} used in a {{gli|analytical chemistry|chemical analysis}} which reacts with one or more other {{gli|chemical species}} that may interfere in the analysis.}}

{{term|mass}} {{defn|A {{gli|physical property|property}} of physical {{gli|matter}} that is a measure of its resistance to acceleration when a net force is applied. The {{gli|SI}} unit for mass is the kilogram (kg).}}

{{term|mass number (''A'')}}{{anchor|mass number}} {{ghat|Also '''atomic mass number''' or '''nucleon number'''.}} {{defn|The total number of {{gli|protons}} and {{gli|neutrons}} (together known as {{gli|nucleons}}) within the {{gli|nucleus}} of an {{gli|atom}}. It determines the {{gli|atomic mass}} of the atom. Mass number varies between different {{gli|isotopes}} of the same chemical element, and is often included either after the element's name (as in carbon-12) or as a superscript to the left of the element's symbol (as in 12C) to identify a specific isotope.}}

{{term|mass spectrometry (MS)}} {{defn|An analytical technique that measures the mass-to-charge ratio of {{gli|ions}} in a chemical sample by bombarding the sample with electrons to the point of {{gli|ionization}} and then separating the charged fragments by subjecting them to an electric or magnetic field, typically in order to determine the elemental or {{gli|isotopic signature|isotopic signatures}} of an unknown substance, the {{gli|mass|masses}} of its constituent particles, and/or the identities or structures of the molecules within it. The results are presented as a mass spectrum, a plot of the intensity of ion signals as a function of the mass-to-charge ratio.}}

{{term|matter}} {{defn|Any substance that has {{gli|mass}} and takes up space by having {{gli|volume}}.}}

{{term|metal}}{{anchor|metals|metallic}} {{defn|Any chemical element which is a good {{gli|conductor}} of both {{gli|electricity}} and {{gli|heat}} and which readily forms {{gli|cations}} and {{gli|ionic bonds}} with {{gli|non-metals}}.}}

{{term|melting}}{{anchor|melt|melts|melted}} {{defn|The {{gli|phase transition}} of a substance from a {{gli|solid}} to a {{gli|liquid}}.}}

{{term|melting point}}{{anchor|melting points}} {{ghat|Also '''liquefaction point'''.}} {{defn|The {{gli|temperature}} at which a substance changes {{gli|state}} from a {{gli|solid}} to a {{gli|liquid}}. It depends on {{gli|pressure}} and is usually specified for a given substance under {{gli|standard temperature and pressure|standard conditions}}. The melting point of a substance is identical to its {{gli|freezing point}}.}}

{{term|mercaptan}} {{defn|See ''{{gli|thiol}}''.}}

{{term|mercapto}} {{defn|See ''{{gli|thiol}}''.}}

{{term|metalloid}}{{anchor|metalloids}} {{defn|A {{gli|chemical element}} or {{gli|substance}} possessing properties of both {{gli|metals}} and {{gli|non-metals}}.}}

{{term|metamer}} {{defn|See ''{{gli|isomer}}''.}}

{{term|metathesis}} {{defn|A class of chemical reaction involving the exchange of elements or functional groups between two or more compounds, as described by the general equation <math display="inline">\mathrm{{AX} + {BY}} \rightarrow \mathrm{{AY} + {BX}}</math>.<ref name="McGraw-Hill"/> Examples include alkane metathesis, alkyne metathesis, olefin metathesis, and salt metathesis reaction. See also ''{{gli|double displacement}}''.}}

{{term|methyl}} {{ghat|Also '''carbinyl'''.}} {{defn|The {{gli|alkyl}} {{gli|functional group}} derived from methane, consisting of one carbon atom bonded to three hydrogen atoms, with the chemical formula {{chem|CH|3}}. It is the simplest {{gli|hydrocarbon}} and occurs as a {{gli|substituent}} in numerous organic compounds, though it may also exist independently as an ion or radical. In {{gli|IUPAC}} nomenclature, the presence of a methyl substituent is indicated with the prefix ''methyl'' in the name of the compound, or with the abbreviation ''Me'' in chemical formulae; e.g. methyl alcohol (methanol) is often written with the formula {{chem|CH|3|OH}} or {{chem|Me|OH}}.}} thumb|right|350px|Various ways of depicting a '''{{gli|methyl}}''' group in structural formulae

{{term|methylene blue}} {{defn|A {{gli|heterocyclic ring|heterocyclic}} {{gli|aromatic}} {{gli|compound}} with the {{gli|molecular formula}} {{gli|carbon|C}}16{{gli|hydrogen|H}}18{{gli|nitrogen|N}}3S Cl.}}

{{term|microcentrifuge tube}}{{anchor|microcentrifuge tubes|microtube|microtubes}} {{defn|A small plastic, sealable container that is used to store small volumes of liquid, generally less than 2 milliliters.}} [[File:Coomassie solution.jpg|thumb|right|350px|A 1.7-milliliter '''{{gli|microcentrifuge tube}}''' or {{gli|Eppendorf tube}} containing Coomassie Blue solution]]

{{term|mineral}}{{anchor|minerals}} {{defn|A {{gli|solid}} {{gli|chemical compound}} with a fairly well-defined {{gli|chemical composition}} and a specific {{gli|crystal|crystal structure}} that occurs naturally in pure form.<ref name=raff>John P. Rafferty, ed. (2011): ''[https://books.google.com/books?id=ervUafk86MIC Minerals]''; p. 1. In the series ''Geology: Landforms, Minerals, and Rocks''. Rosen Publishing Group. {{ISBN|978-1615304899}}</ref>}}

{{term|miscibility}}{{anchor|miscible|immiscible}} {{defn|The tendency or capability of two or more substances to blend uniformly when combined (most commonly liquids, though the concept is also applicable to solids and gases), i.e. to {{gli|dissolve}} in each other, forming a homogeneous {{gli|mixture}} that exists in a single {{gli|phase}}, without separation of phases, regardless of the proportions of each substance. Substances that do not mix uniformly in all proportions are said to be ''immiscible''.<ref name="McGraw-Hill"/><ref name="Gold Book"/>}}

{{term|mixture}}{{anchor|mixtures}} {{defn|A material made up of two or more different substances which are mixed physically but are not combined chemically (i.e. a chemical reaction has not taken place which has changed the molecules of either substance into new substances).}}

{{term|moiety}}{{anchor|moieties}} {{defn|Any named characteristic group, branch, or other part of a large {{gli|molecule}} that may be identified within other kinds of molecules as well. {{gli|functional group|Functional groups}} are typically smaller and more generic than moieties, whereas {{gli|substituents}} and {{gli|side chains}} may often be classified as moieties and vice versa.}}

{{term|molal concentration}}{{anchor|molality|molal}} {{ghat|Also '''molality'''.}} {{defn|A measure of the {{gli|concentration}} of a {{gli|solute}} in a {{gli|solution}} in terms of the {{gli|amount}} of solute per unit {{gli|mass}} of {{gli|solvent}}. Molality is typically expressed in units of {{gli|moles}} per {{gli|kilogram}} (mol/kg); a solution with a concentration of exactly 1 mol/kg is sometimes said to be ''1 molal''. Contrast ''{{gli|molarity}}''.}}

{{term|molar concentration}}{{anchor|molarity|molar}} {{ghat|Also '''molarity''', '''amount concentration''', or '''substance concentration'''.}} {{defn|A measure of the {{gli|concentration}} of a {{gli|chemical species}}, especially of a {{gli|solute}} in a {{gli|solution}}, in terms of the {{gli|amount}} of the species per unit {{gli|volume}} of solution. Molarity is typically expressed in units of {{gli|moles}} per {{gli|litre}} (mol/L); a solution with a concentration of exactly 1 mol/L is commonly said to be ''1 molar'', abbreviated ''1 M''. Contrast ''{{gli|molality}}''.}}

{{term|molar fraction}} {{ghat|Also '''mole fraction'''.}} {{defn|}}

{{term|molar mass}} {{ghat|Sometimes used interchangeably with '''{{gli|molecular weight}}''' and '''{{gli|formula weight}}'''.}} {{defn|For a given {{gli|chemical compound}}, the {{gli|mass}} of a sample of that compound divided by the {{gli|amount}} of compound in the sample, usually expressed in {{gli|grams}} per {{gli|mole}} (g/mol). As a bulk property, molar mass is an average of the masses of many instances of the compound, each of which may vary slightly due to the presence of {{gli|isotopes}} of the compound's constituent atoms; it is commonly derived from the compound's {{gli|molecular weight}}, which itself is a sum of the {{gli|standard atomic weights}} of the constituent atoms, and is therefore a function of the relative abundance of the isotopes as they occur naturally on Earth. Molar mass allows easy conversion between mass and number of moles when considering bulk quantities of a substance.}}

{{term|molarity}} {{defn|See ''{{gli|molar concentration}}''.}}

{{term|mole (mol)}}{{anchor|mole|moles|mol}} {{defn|A unit (symbol: mol) used to measure the {{gli|amount}} of a {{gli|substance}} in terms of the absolute number of particles or entities composing the substance. By definition, one mole of any substance contains exactly the {{gli|Avogadro number}} (i.e. 6.022{{e|23}}) of particles or entities.}}

{{term|molecular orbital (MO)}}{{anchor|molecular orbital|molecular orbitals}} {{defn|Any region in which one or more {{gli|electrons}} may be found in a {{gli|molecule}} (as opposed to that within {{gli|atomic orbital|an individual atom}}).}}

{{term|molecule}}{{anchor|molecules|molecular}} {{defn|A number of {{gli|atoms}} that are chemically {{gli|bonded}} together and collectively electrically neutral.}}

{{term|monatomic}} {{defn|Having only one {{gli|atom}}, as opposed to a {{gli|molecule}} composed of more than one. Virtually all elements are monatomic in the {{gli|gas}} phase at sufficiently high temperatures. Contrast ''{{gli|diatomic}}'' and ''{{gli|polyatomic}}''.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== N == {{glossary}} {{term|natural abundance}} {{defn|}}

{{term|neat}} {{defn|Conditions with a liquid {{gli|reagent}} or gas performed with no added solvent or cosolvent.}}

{{term|neutron}}{{anchor|neutrons}} {{defn|A type of {{gli|subatomic particle}} that is electrically neutral, having no net charge.}}

{{term|noble gas}}{{anchor|noble gases|inert gas|inert gases}} {{ghat|Also '''inert gas'''.}} {{defn|Any of the six {{gli|non-metal|non-metallic}} {{gli|elements}} of {{gli|group|Group 18}} of the {{gli|periodic table}}: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). All of the noble gases have outer {{gli|electron shells}} that are completely filled with {{gli|valence electrons}} in their naturally occurring states, giving them very low or {{gli|inert|negligible chemical reactivity}}.}}

{{term|non-metal}}{{anchor|non-metals|non-metallic}} {{defn|Any chemical element which is not a {{gli|metal}}.}}

{{term|nonpolar compound}} {{defn|A {{gli|compound}} consisting of {{gli|covalent}} {{gli|molecules}} with no permanent {{gli|dipole moment}}.<ref name="Daintith"/> Contrast ''{{gli|polar compound}}''.}}

{{term|nuclear}} {{defn|Of or pertaining to the {{gli|nucleus|atomic nucleus}}.}}

{{term|nuclear chemistry}} {{defn|The branch of chemistry that studies the various processes and properties relevant to {{gli|nucleus|atomic nuclei}}, including {{gli|radioactivity}}.}}

{{term|nuclear magnetic resonance spectroscopy}} {{defn|A technique that exploits the magnetic properties of certain atomic nuclei, useful for identifying unknown compounds. Nuclear magnetic resonance is often abbreviated ''NMR''.}}

{{term|nucleon}}{{anchor|nucleons}} {{defn|Either a {{gli|proton}} or a {{gli|neutron}}, considered in its role as a component of an {{gli|nucleus|atomic nucleus}}.}}

{{term|nucleophile}}{{anchor|nucleophiles|nucleophilic}} {{defn|Any atom or molecule which can donate an {{gli|electron pair}} to another atom or molecule. All molecules or ions with a free pair of electrons or at least one {{gli|pi bond}} can act as nucleophiles, by which they are attracted to {{gli|electron deficiency|electron-deficient}} regions of other species; a chemical reaction involving a nucleophile donating an electron pair to an {{gli|electrophile}} may be referred to as ''nucleophilic attack''. Because they donate electrons, nucleophiles are {{gli|Lewis bases}} by definition.}}

{{term|nucleus}}{{anchor|nuclei|atomic nucleus|atomic nuclei}} {{defn|The centre of an {{gli|atom}}, made up of {{gli|neutrons}} and {{gli|protons}} and possessing a net positive electric charge.}}

{{term|nuclide}}{{anchor|nuclides}} {{defn|A species of {{gli|atom}} characterized by its {{gli|mass number}}, {{gli|atomic number}}, and nuclear energy state, provided that the mean life in that state is long enough to be observable.}}

{{term|number density}} {{defn|A measure of the {{gli|concentration}} of countable objects (atoms, molecules, etc.) in space, expressed as the number per unit {{gli|volume}}.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== O == {{glossary}} {{term|octet rule}} {{ghat|Also '''Lewis octet rule'''.}} {{defn|A classical rule for describing the {{gli|electron configuration}} of atoms in certain molecules: the maximum number of {{gli|electron pairs}} that can be accommodated in the {{gli|valence electron|valence}} {{gli|electron shell|shell}} of an element in the first row of the {{gli|periodic table}} is four (or eight total electrons). For elements in the second and subsequent rows, there are many exceptions to this rule.}}

{{term|olefin}} {{defn|A trivial (non-{{gli|IUPAC}}) name for any {{gli|alkene}}.}}

{{term|orbital}}{{anchor|orbitals}} {{defn|Any region of an atom or molecule in which one or more {{gli|electrons}} can be found. The term may refer to either an {{gli|atomic orbital}} or a {{gli|molecular orbital}}.}}

{{term|orbital hybridisation}} {{ghat|Also '''orbital hybridization'''.}} {{defn|}}

{{term|organic acid}} {{defn|Any {{gli|organic compound}} with {{gli|acidic}} properties. Contrast ''{{gli|organic base}}''.}}

{{term|organic base}} {{defn|Any {{gli|organic compound}} with {{gli|basic}} properties. Contrast ''{{gli|organic acid}}''.}}

{{term|organic chemistry}} {{defn|The branch of chemistry concerned with the chemical properties and reactions of {{gli|organic compounds}}. Contrast ''{{gli|inorganic chemistry}}''.}}

{{term|organic compound}}{{anchor|organic compounds|organic}} {{defn|Any {{gli|chemical compound}} that contains one or more {{gli|carbon}} atoms. Contrast ''{{gli|inorganic compound}}''.}}

{{term|organosulfur compound}} {{defn|Any {{gli|chemical compound}} which contains both {{gli|carbon}} and sulfur atoms.<ref name="McGraw-Hill"/>}}

{{term|osmole}} {{defn|}}

{{term|osmosis}} {{defn|The spontaneous net movement or {{gli|diffusion}} of molecules of a {{gli|solvent}} (e.g. {{gli|water}}) through a {{gli|selectively permeable membrane}} separating two {{gli|solutions}} with different {{gli|concentrations}} of dissolved {{gli|solutes}}, in the direction that tends to equalize the solute concentrations on the two sides, i.e. from the more dilute solution to the more concentrated solution, or, equivalently, from a region of high {{gli|water potential}} to a region of low water potential. Because the solute is unable to cross the membrane, the tendency towards equilibration compels the solvent to cross the membrane instead. This continues until an equilibrium is reached, where neither side of the membrane is more or less concentrated than the other.}} thumb|right|350px|During '''{{gli|osmosis}}''', the transfer of solvent molecules out of the more dilute solution (in the left beaker, on the left side of the membrane) increases that solution's solute concentration, while the simultaneous addition of solvent to the more concentrated solution on the other side of the membrane decreases its own concentration. The eventual result is an equilibrium of the solute concentrations on both sides of the membrane, though the volumes on each side are no longer equal (right beaker).

{{term|other metal}} {{defn|Any of the {{gli|metallic}} elements in the {{gli|p-block}}, which are characterized by having a combination of relatively low {{gli|melting points}} (all less than 950 K) and relatively high {{gli|electronegativity}} values (all more than 1.6, revised Pauling).}}

{{term|oxidation}} {{defn|The increase in the {{gli|oxidation state}} of a chemical species in a {{gli|redox}} reaction, generally by losing {{gli|electrons}}. Contrast ''{{gli|reduction}}''.}}

{{term|oxidation state}} {{ghat|Also '''oxidation number'''.}} {{defn|no=1|The degree of {{gli|oxidation}} of an individual atom in a chemical compound, measured as the decrease in the number of {{gli|electrons}} relative to the atom's naturally occurring {{gli|elemental}} state.}} {{defn|no=2|The hypothetical {{gli|electric charge}} (positive, negative, or zero) that an atom would have if all bonds to atoms of different elements were 100% {{gli|ionic}}, with no {{gli|covalent}} component.}}

{{term|oxidizing agent}}{{anchor|oxidizing agents}} {{ghat|Also '''oxidant''', '''oxidizer''', or '''electron acceptor'''.}} {{defn|no=1|A chemical species that gains or accepts one or more {{gli|electrons}} from another species, called the {{gli|reducing agent}}, in a {{gli|redox}} reaction, thereby causing the {{gli|oxidation}} of the other species and in turn being itself {{gli|reduced}}. The oxidizing agent's {{gli|oxidation state}} decreases, while the reducing agent's increases.<ref name="Daintith"/>}} {{defn|no=2|A chemical species that transfers strongly {{gli|electronegative}} {{gli|atoms}}, usually oxygen, to a substrate.}}

{{term|oxoacid}}{{anchor|oxoacids}} {{ghat|Also '''oxyacid''' or '''oxacid'''.}} {{defn|no=1|Any {{gli|acid}} having {{gli|oxygen}} in the acidic group.}} {{defn|no=2|Any compound which contains oxygen, at least one other element, and at least one {{gli|hydrogen}} atom bound to oxygen, and which produces a {{gli|conjugate base}} by the loss of positively charged hydrogen {{gli|protons}}.}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== P == {{glossary}} {{term|p-block}} {{defn|}}

{{term|paired electron}}{{anchor|paired electrons}} {{defn|One of two {{gli|electrons}} that together form a {{gli|valence bonding|valence bond}} between two {{gli|atoms}}.<ref name="McGraw-Hill"/> Contrast ''{{gli|unpaired electron}}''.}}

{{term|paraffin}}{{anchor|paraffins}} {{defn|no=1|A trivial (non-{{gli|International Union of Pure and Applied Chemistry|IUPAC}}) name for any {{gli|alkane}}.}} {{defn|no=2|Another name for kerosene.}}

{{term|pascal (Pa)}} {{defn|}}

{{term|passivation}} {{defn|The process of coating a substance with a thin layer of a protective material, often a {{gli|metal oxide}}, to create a shield against {{gli|corrosion}} or other chemical reactions with the environment, thereby rendering the coated substance "passive" or less susceptible to undesirable reactions.}}

{{term|passivity}} {{defn|A state of chemical inactivity, especially of a {{gli|metal}} that is relatively resistant to {{gli|corrosion}} due to natural or induced loss of chemical reactivity (as with {{gli|passivation}}).<ref name="McGraw-Hill"/> See also ''{{gli|inert}}''.}}

{{term|pendant group}}{{anchor|pendant groups|pendant}} {{defn|An offshoot or {{gli|side chain}} of the {{gli|backbone}} of a {{gli|polymeric}} molecule, especially one which is itself neither oligomeric or polymeric.<ref name="Gold Book"/>}}

{{term|pentabasic}} {{defn|(of a chemical compound) Having five {{gli|hydrogen}} atoms which may be replaced by {{gli|metals}} or {{gli|bases}}.<ref name="McGraw-Hill"/>}}

{{term|pentoxide}} {{defn|Any {{gli|binary compound}} containing five atoms of oxygen, e.g. iodine pentoxide ({{chem|I|2|O|5}}).<ref name="McGraw-Hill"/>}}

{{term|pentyl}} {{ghat|Also '''amyl'''.}} {{defn|An {{gli|alkyl}} {{gli|functional group}} containing five carbon atoms, with the generic chemical formula –{{chem|C|5|H|11}}. It is the {{gli|substituent}} form of the {{gli|alkane}} pentane.}}

{{term|per-}} {{defn|A prefix in {{gli|IUPAC}} chemical nomenclature meaning complete, exhaustive, or extreme, as in a completely {{gli|substituent|substituted}} {{gli|hydrocarbon}}; or indicating the presence of a {{gli|peroxy}} group.<ref name="McGraw-Hill"/>}}

{{term|peracid}} {{defn|An {{gli|acid}} containing an acidic {{gli|peroxy}} group ({{chem|–O–O–}}); e.g. periodic acid.<ref name="McGraw-Hill"/>}}

{{term|period}}{{anchor|period|periods}} {{defn|A horizontal row of the {{gli|periodic table of the elements}} and the elements that share it. Contrast ''{{gli|group}}''.}}

{{term|periodic table of the elements}}{{anchor|periodic table of the elements|periodic table}} {{ghat|Also simply the '''periodic table'''.}} {{defn|A tabular arrangement of the {{gli|chemical elements}} organized by their {{gli|atomic number}}, {{gli|electron configuration}}, and other chemical properties, whose adopted structure shows periodic trends and is used by chemists to derive relationships between various elements as well as predict the properties and behaviors of undiscovered or newly synthesized elements. The first periodic table of the elements was published by Russian chemist Dmitri Mendeleev in 1869.}} thumb|right|350px|The modern '''{{gli|periodic table|periodic table of the elements}}'''. The horizontal rows are called {{gli|periods}} and the vertical columns are called {{gli|groups}} or families.

{{term|peroxide}}{{anchor|peroxides}} {{defn|no=1|A class of compounds which contain a {{gli|peroxy}} group, having the generic {{gli|structural formula}} {{chem|R–O–O–R}}, where R is any element or {{gli|functional group}}; e.g. hydrogen peroxide (empirically {{chem|H|2|O|2}}, structurally {{chem|H–O–O–H}}).<ref name="McGraw-Hill"/>}} {{defn|no=2|Another name for the peroxy group itself.}} {{defn|no=3|A {{gli|salt}} of the {{gli|anion}} {{chem|O|2|2-}}.<ref name="Gold Book"/>}}

{{term|peroxy}} {{ghat|Also '''peroxide''' and sometimes '''peroxo'''.}} {{defn|A {{gli|functional group}} consisting of two {{gli|oxygen}} atoms directly connected to each other by a {{gli|single bond}} and each also connected to one other atom. Peroxides have the general structural formula {{chem|–O–O–}}.}}

{{term|pH}} {{defn|defn=A logarithmic scale used to specify the {{gli|acid|acidity}} or {{gli|base|basicity}} of an {{gli|aqueous solution}}. The pH scale approximates the negative of the base-10 logarithm of the {{gli|molar concentration}} of {{gli|hydrogen}} {{gli|ions}} in a solution. At {{gli|room temperature}}, pure water is neutral (pH = 7); solutions with a pH less than 7 are acidic and those with a pH greater than 7 are basic.}}

{{term|phase}}{{anchor|phases}} {{defn|A region of space throughout which all physical properties of a substance are essentially uniform, or a region of material that is chemically uniform, physically distinct, and often mechanically separable. The term ''phase'' may have several different uses in chemistry contexts; colloquially, it is often used interchangeably with {{gli|state of matter}}, but many distinct phases may exist within a single state of matter.}}

{{term|phase diagram}} {{defn|A graphical representation of the equilibrium relationships between {{gli|thermodynamics|thermodynamically}} distinct {{gli|phases}} of a chemical compound, mixture, or solution, indicating the physical conditions (e.g. temperature and pressure) under which various phases (e.g. {{gli|solid}}, {{gli|liquid}}, and {{gli|vapor}}) occur or coexist.<ref name="McGraw-Hill"/>}}

{{term|phase transition}} {{defn|no=1|A transformation of a {{gli|chemical substance}} between {{gli|solid}}, {{gli|liquid}}, and {{gli|gas|gaseous}} {{gli|state of matter|states of matter}} and, in rare cases, {{gli|plasma|plasma}}.}} {{defn|no=2|The measurable values of the external conditions at which such a transformation occurs.}} thumb|right|350px|This diagram shows the nomenclature commonly used for each of the different '''{{gli|phase transition|phase transitions}}'''.

{{term|phenyl}} {{defn|A {{gli|functional group}} consisting of a {{gli|cyclic}} ring of six carbon atoms with the chemical formula {{chem|–C|6|H|5}}. It is the {{gli|substituent}} form of the {{gli|cycloalkane}} benzene.}}

{{term|photon}}{{anchor|photons}} {{defn|A carrier of {{gli|electromagnetic radiation}} of all wavelengths (such as gamma rays and radio waves).}}

{{term|physical chemistry}} {{defn|The branch of chemistry that studies chemical systems in terms of the principles, practices, and concepts of physics, such as motion, energy, force, time, thermodynamics, {{gli|chemical equilibrium}}, and statistical mechanics, among others. In contrast to {{gli|chemical physics}}, physical chemistry is predominantly (though not entirely) a macroscopic science that studies the physical and chemical interactions of bulk quantities of matter.}}

{{term|pipette}}{{anchor|pipettes|pipet|pipets}} {{ghat|Also spelled '''pipet'''.}} {{defn|A laboratory tool commonly used in chemistry, biology, and medicine to transfer and dispense a precisely measured volume of liquid.}}

{{term|plasma}} {{defn|One of the four fundamental {{gli|states of matter}}, in which very high-energy particles are partially or fully {{gli|ionization|ionized}} to the point that they display unique properties and behaviors unlike those of the other three states. Plasma does not exist freely on the Earth's surface under natural conditions.}}

{{term|pnictogen}} {{defn|Any of the chemical {{gli|elements}} belonging to {{gli|nitrogen family|Group (V)}} of the {{gli|periodic table}}: nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and moscovium (Ms). These elements are united by their common pentavalency; i.e. in their non-ionized states, atoms of these elements all have exactly five {{gli|valence electrons}} in their outermost {{gli|electron shell}}, three short of a complete {{gli|octet}}.}}

{{term|polyatomic}} {{defn|Composed of two or more atoms, of the same or different elements. Contrast ''{{gli|monatomic}}'' and ''{{gli|diatomic}}''.}}

{{term|polyatomic ion}} {{defn|A {{gli|molecule}} composed of two or more {{gli|covalently bonded}} {{gli|atoms}} which collectively bear a net {{gli|electric charge}} and therefore act as an {{gli|ion}}.}}

{{term|polymerization}}{{anchor|polymerize|polymerizes|polymerizing|polymerized}} {{defn|The chemical bonding of two or more individual {{gli|monomer}} molecules to form a {{gli|polymer}} chain or network; or any reaction that produces such a bonding.<ref name="McGraw-Hill"/>}}

{{term|potential energy}} {{defn|The stored energy in a body or in a system due to its position in a force field or due to its configuration.}}

{{term|precipitant}} {{defn|A chemical compound or {{gli|reagent}} that causes a chemical reaction resulting in the formation of a solid {{gli|precipitate}} when added to a {{gli|solution}}.<ref name="McGraw-Hill"/>}}

{{term|precipitate}} {{defn|no=1|(n.) A solid substance that separates from a liquid solution or {{gli|diffuses}} out of a solid {{gli|alloy}} during the process of {{gli|precipitation}}.<ref name="McGraw-Hill"/>}} {{defn|no=2|(v.) To separate from another substance by forming a distinct, condensed solid {{gli|phase}}.}}

{{term|precipitation}} {{defn|The process of producing a separable {{gli|solid}} {{gli|phase}} within a {{gli|liquid}} medium, e.g. by transforming the dissolved {{gli|solute}} of a supersaturated {{gli|solution}} into an insoluble solid; or the {{gli|diffusion}} of a distinct solid phase out of a solid {{gli|alloy}}. A reagent that causes such a reaction is called the {{gli|precipitant}}, and the separable solid itself is the {{gli|precipitate}}.<ref name="McGraw-Hill"/> More generally, the term may refer to the formation of any new condensed phase by changing the physical properties of a system (e.g. {{gli|water vapor}} condensing into liquid water droplets).}}

{{term|precision}} {{defn|How close the results of multiple experimental trials or observations are to each other. Compare ''{{gli|accuracy}}''.}}

{{term|pressure}} {{defn|The force applied perpendicular to the surface of an object per unit area. The {{gli|SI}} unit for pressure is the {{gli|pascal}} (Pa), though many other units of pressure are also commonly used in chemistry.}}

{{term|primary}} {{defn|The simplest, most commonly known, or canonical form of a chemical compound with multiple similar or {{gli|isomeric}} forms. For example, in a primary alcohol, the carbon is bonded to a single {{gli|substituent}} group ({{chem|R|1|C|H|2|OH}}), whereas a secondary alcohol is doubly substituted ({{chem|R|1|R|2|C|H|OH}}) and a tertiary alcohol is triply substituted ({{chem|R|1|R|2|R|3|C|OH}}).<ref name="McGraw-Hill"/>}}

{{term|propyl}} {{defn|The {{gli|alkyl}} {{gli|functional group}} derived from either of the two isomers of propane, with the generic chemical formula –{{chem|C|3|H|7}}. It may occur as a {{gli|substituent}} in organic compounds or exist independently as an ion or radical. In {{gli|IUPAC}} nomenclature, the presence of a propyl substituent is indicated with the prefix ''propyl'' in the name of the compound, or with the abbreviation ''Pr'' in chemical formulae; e.g. propyl alcohol (propanol) may occur in either of two isomeric forms, either the linear 1-propanol or ''n''-propanol, written {{chem|CH|3|CH|2|CH|2|OH}}, or the branched 2-propanol or isopropyl alcohol, written {{chem|(|CH|3|)|2|CHOH}}, and both forms may be written with the generic formula {{chem|Pr|OH}}. A third, non-isomeric, {{gli|cyclic}} form known as cyclopropyl is also sometimes considered a propyl group.}}

{{term|protic}} {{ghat|Also '''protogenic'''.}} {{defn|(of a chemical species) Capable of acting as a {{gli|proton}} donor; readily generating or yielding free protons ({{chem|H|+}}) in solution. Protic species may therefore be considered strongly or weakly {{gli|acidic}} in the sense of a {{gli|Brønsted–Lowry acid}}.<ref name="Gold Book"/>}}

{{term|proton}}{{anchor|protons}} {{defn|A {{gli|subatomic particle}} with a positive electric charge that is found in the {{gli|nucleus}} of an {{gli|atom}}. Often denoted with the symbol {{chem|H|+}}.}}

{{term|protonation}}{{anchor|protonate|protonates|protonating|protonated}} {{defn|The addition of a {{gli|proton}} ({{chem|H|+}}) to an atom, molecule, or ion.}}

{{term|pure substance}} {{defn|See ''{{gli|chemical substance}}''.}}

{{term|pyrochemistry}} {{defn|The study of chemical reactions that occur at high temperatures.}}

{{term|pyrolysis}} {{defn|The thermal decomposition of materials at elevated temperatures in an {{gli|inert}} atmosphere such as a vacuum gas.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== Q == {{glossary}} {{term|quantum}}{{anchor|quanta}} {{ghat|(pl.) '''quanta'''}} {{defn|}}

{{term|quantum mechanics}} {{defn|The study of how atoms, molecules, {{gli|subatomic particles}}, etc. behave and are structured.}}

{{term|quark}}{{anchor|quarks}} {{defn|An elementary particle and a fundamental constituent of matter.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== R == {{glossary}} {{term|racemate}} {{defn|An {{gli|equimolar}} {{gli|mixture}} of a pair of {{gli|enantiomer|enantiomers}} which does not exhibit {{gli|optical activity}}. The chemical name or formula of a racemate is distinguished from those of the enantiomers by the prefix (±)- or by the symbols ''RS'' and ''SR''.}}

{{term|radiation}} {{defn|Energy released in the form of waves or {{gli|subatomic particle|subatomic particles}} when there is a change from high-energy to low-energy states.}}

{{term|radical}}{{anchor|radicals|free radical|free radicals}} {{ghat|Also '''free radical'''.}} {{defn|Any atom, molecule, or ion that has at least one {{gli|unpaired electron|unpaired}} {{gli|valence electron}}. With few exceptions, such unpaired electrons make radicals highly chemically reactive, and therefore organic radicals are usually short-lived.}}

{{term|radioactive decay}} {{defn|The process by which an unstable atomic {{gli|nucleus}} loses excess nuclear energy by emitting {{gli|radiation}} in any of several forms, including as {{gli|gamma radiation}}, as {{gli|alpha particle|alpha}} or {{gli|beta particles}}, or by ejecting {{gli|electrons}} from its atomic {{gli|orbitals}}.}}

{{term|radiochemistry}} {{defn|The branch of chemistry involving the study of radioactive substances and {{gli|radioactivity}}, including the use of radioactive {{gli|isotopes}} to study non-radioactive isotopes and ordinary chemical reactions.}}

{{term|radionuclide}} {{ghat|Also '''radioisotope'''.}} {{defn|A {{gli|radioactive}} {{gli|nuclide}} of a specified {{gli|element}}, especially a particular {{gli|isotope}} of that element which characteristically undergoes spontaneous {{gli|radioactive decay|decay}} into one or more {{gli|stable nuclides}} by emitting excess energy from the nucleus.<ref name="Gold Book"/>}}

{{term|Raoult's law}} {{defn|A law of thermodynamics which states that the {{gli|partial pressure}} of each {{gli|gaseous}} component of an {{gli|ideal solution|ideal mixture}} of {{gli|liquids}} is equal to the {{gli|vapor pressure}} of the pure component multiplied by its {{gli|molar fraction}} in the mixture.}}

{{term|rare-earth element}} {{ghat|Also called '''rare-earth metals''' or used interchangeably with '''{{gli|lanthanides}}'''.}} {{defn|Any of the 17 nearly indistinguishable, silvery-white, soft, {{gli|heavy metal|heavy}} {{gli|metal|metallic}} {{gli|elements}} belonging to a set including the {{gli|lanthanide}} series (atomic numbers 57 through 71) as well as scandium and yttrium.}}

{{term|rate-determining step}} {{ghat|Also '''rate-limiting step'''.}} {{defn|The slowest step in a {{gli|chemical reaction}} that involves more than one step. The rate of this step determines the overall {{gli|reaction rate}}.<ref name="Daintith"/>}}

{{term|reactant}}{{anchor|reactants}} {{ghat|Sometimes used interchangeably with '''{{gli|reagent}}'''.}} {{defn|Any substance that is consumed in the course of a {{gli|chemical reaction}}.}}

{{term|reaction}} {{defn|See ''{{gli|chemical reaction}}''.}}

{{term|reaction barrier}} {{defn|The energy deficit that must be overcome in order for a particular {{gli|chemical reaction}} to proceed. In {{gli|transition state theory}}, the reaction barrier is interpreted as the difference between the {{gli|zero-point energy}} of the {{gli|activated complex}} formed in the reaction and that of the initial {{gli|reactants}}.<ref name="Gold Book"/> See also ''{{gli|activation energy}}''.}}

{{term|reaction mechanism}} {{defn|The step-by-step sequence of {{gli|elementary reaction|elementary reactions}} by which a larger {{gli|chemical reaction}} or overall change occurs. A complete mechanism must describe and explain which {{gli|bond|bonds}} are broken and which are formed (and in what order), as well as all {{gli|reactant|reactants}}, {{gli|product|products}}, and {{gli|catalyst|catalysts}} involved; the amounts of each; all {{gli|reactive intermediate|intermediates}}, {{gli|activated complex|activated complexes}}, and {{gli|transition state|transition states}}; and the {{gli|stereochemistry}} of each chemical species. Because the detailed processes of a complex reaction are not observable in most cases, a reaction mechanism is often a theoretical conjecture based on thermodynamic feasibility and what little support can be gained from experiment.}}

{{term|reaction rate}} {{defn|The speed at which {{gli|reactant|reactants}} are converted into {{gli|product|products}} in a {{gli|chemical reaction}}.}}

{{term|reactive bond}} {{defn|A {{gli|chemical bond}} between atoms which, in a particular context, is relatively unstable and therefore easily broken or invaded by other {{gli|chemical species}} or {{gli|radicals}}; e.g. the {{gli|double bond}} in ethylene ({{chem|C|H|2|{{=}}C|H|2}}) is highly reactive in the presence of other ethylene molecules, leading to a {{gli|polymerization}} reaction that forms polyethylene.<ref name="McGraw-Hill"/>}}

{{term|reactive intermediate}}{{anchor|reactive intermediates|intermediate|intermediates}} {{ghat|Also simply '''intermediate'''.}} {{defn|Any short-lived, unstable, highly reactive {{gli|chemical species}} which is generated briefly in a {{gli|chemical reaction}} but rapidly undergoes further reactions that transform it into a more stable species. It is thus a transient intermediary between the stable {{gli|reactants}} and {{gli|products}} of the overall reaction. The existence of intermediates, when detectable, is critical to an accurate understanding of a {{gli|reaction mechanism}}.}}

{{term|reactivity}} {{defn|The tendency of a particular {{gli|chemical substance}} to undergo a {{gli|chemical reaction}}, either by itself or with other substances, generally referring to either or both of two distinct observations: whether or not a substance reacts under a specific set of circumstances, and how quickly it reacts (i.e. the {{gli|reaction rate}}). {{gli|thermodynamics|Thermodynamically}}, a chemical reaction occurs because the {{gli|product|products}} (taken as a group) exist at a lower {{gli|free energy}} than the {{gli|reactant|reactants}}, and hence are more energetically "stable", but the concept of reactivity may also embody {{gli|kinetics|kinetic}} factors, depending on the usage. {{gli|chemical stability|Chemical stability}} and {{gli|chemical compatibility}} are related but distinct concepts.}}

{{term|reactivity series}} {{ghat|Also '''activity series'''.}} {{defn|An empirical, calculated, and structurally analytical progression of a series of {{gli|metals}}, arranged by their general {{gli|reactivity}} from highest to lowest and used to summarize information about their reactions with {{gli|acids}} and water and the methods used to extract them from ores.}}

{{term|reagent}}{{anchor|reagents}} {{defn|no=1|Another name for a {{gli|reactant}}.}} {{defn|no=2|A test substance that is added to a system in order to bring about a {{gli|chemical reaction}}, or to see whether a reaction occurs.}}

{{term|reducing agent}} {{ghat|Also '''reductant''', '''reducer''', or '''electron donor'''.}} {{defn|A chemical species that loses or donates one or more {{gli|electrons}} to another species, called the {{gli|oxidizing agent}}, in a {{gli|redox}} reaction, thereby causing the {{gli|reduction}} of the other species and in turn being itself {{gli|oxidation|oxidized}}. The reducing agent's {{gli|oxidation state}} increases, while the oxidizing agent's decreases.<ref name="Daintith"/>}}

{{term|reduction}} {{defn|The decrease in the {{gli|oxidation state}} of a chemical species in a {{gli|redox}} reaction, generally by gaining {{gli|electrons}}. Contrast ''{{gli|oxidation}}''.}}

{{term|refractory}} {{defn|no=1|Having a high {{gli|melting point}}.<ref name="Daintith"/>}} {{defn|no=2|A material that is resistant to {{gli|decomposition}} by heat, pressure, or chemical attack, and retains its strength and form at high temperatures, making it suitable for applications in environments exposed to such conditions. Refractories are usually polycrystalline, polyphase, {{gli|inorganic compound|inorganic}}, non-metallic, porous, and heterogeneous compounds.}}

{{term|retort}} {{defn|A laboratory apparatus used for the {{gli|distillation}} or {{gli|dry distillation}} of chemical substances, traditionally consisting of a spherical vessel with a long, downward-pointing neck that conducts the condensed vapors produced by distillation into a separate collection vessel.}}

{{term|reversible reaction}} {{defn|A {{gli|chemical reaction}} that can proceed in either direction depending on the reaction conditions, i.e. from reactants to products or from products to reactants, especially implying one in which both conversions occur simultaneously. Contrast ''{{gli|irreversible reaction}}''.}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== S == {{glossary}} {{term|s-block}} {{defn|The collective name for the elements in Groups 1 and 2 of the {{gli|periodic table}} (the {{gli|alkali metal|alkali}} and {{gli|alkaline metal|alkaline metals}}), as well as hydrogen and helium.}}

{{term|saline solution}} {{defn|A common term for a {{gli|solution}} of sodium chloride (NaCl) dissolved in water (H2O).}}

{{term|salt}}{{anchor|salts}} {{defn|Any {{gli|ionic compound}} composed of one or more {{gli|anions}} and one or more {{gli|cations}}.}}

{{term|salt bridge}} {{defn|A device used to connect reduction with oxidation half-cells in an {{gli|electrochemical cell}}.}}

{{term|Schrödinger equation}} {{defn|A quantum state equation which represents the behaviour of an electron around an atom.}}

{{term|scintillation}} {{defn|A burst of luminescence of short duration produced by an individual energetically excited particle as it releases energy.<ref name="Gold Book"/>}}

{{term|semiconductor}}{{anchor|semiconductors}} {{defn|An electrically conductive solid whose degree of conductivity lies somewhere between that of a {{gli|conductor}} and that of an {{gli|insulator}}.}}

{{term|side chain}}{{anchor|side chains}} {{defn|A chemical {{gli|substituent|substituent group}} that is attached to the core part or "backbone" of a larger {{gli|molecule}}, especially an oligomeric or polymeric {{gli|hydrocarbon}} chain that branches off of the longer primary chain of a macromolecule. The term is most commonly encountered in {{gli|biochemistry}} and {{gli|organic chemistry}}.}}

{{term|single bond}}{{anchor|single bonds|single-bonded}} {{defn|A {{gli|bond}} that involves the sharing of one {{gli|electron pair|pair of electrons}}.}}

{{term|skeletal formula}} {{defn|}}

{{term|sol}} {{defn|A {{gli|suspension}} of solid particles in a liquid. Artificial examples include sol-gels.}}

{{term|solid}}{{anchor|solids}} {{defn|One of the four fundamental {{gli|states of matter}}, characterized by relatively low-energy particles packed closely together in rigid structures with definite shape and volume. See ''{{gli|Young's modulus|Young's modulus}}''.}}

{{term|solid-phase extraction (SPE)}} {{defn|}}

{{term|solubility}} {{defn|The property of a {{gli|solid}}, {{gli|liquid}}, or {{gli|gaseous}} {{gli|solute}} to {{gli|dissolve}} in a solid, liquid, or gaseous {{gli|solvent}}. It is typically expressed as the proportion of solute dissolved in the solvent in a fully {{gli|saturated}} {{gli|solution}}.}}

{{term|content=solubility product (<math chem display="inline">K_\ce{s}</math> or <math chem display="inline">K_\ce{sp}</math>)}} {{defn|A measure of the {{gli|solubility}} of an ionic {{gli|solute}}, expressed as the arithmetic product of the {{gli|concentration|concentrations}} of its {{gli|ions}} in a fully saturated solution, with respect to the solute's particular {{gli|dissociation}} {{gli|equilibrium constant|equilibria}} and the particular ions present. For a dissociation equilibrium <math display="inline">\mathrm{{A_x}{B_y}_{(s)}} \leftrightharpoons \mathrm{xA^+_{(aq)}} + \mathrm{yB^-_{(aq)}}</math>, the solubility product of the ionic solute <math display="inline">\mathrm{A_x}\mathrm{B_y}</math> is given by <math chem display="inline">K_\ce{s} = [\ce{A+}]^x[\ce{B-}]^y</math>, where <math chem display="inline">[\ce{A+}]</math> and <math chem display="inline">[\ce{B-}]</math> are the concentrations of the solute's ionic constituents in a saturated solution. The solubility product is derived from and functions like the equilibrium constant of dissociation, though unlike an equilibrium constant it is not dimensionless. If the product of ionic concentrations in a solution exceeds the solubility product, then {{gli|precipitation}} occurs.<ref name="Daintith"/>}}

{{term|solute}}{{anchor|solutes}} {{defn|The part of a {{gli|solution}} that is dissolved into the {{gli|solvent}}. For example, sodium chloride (NaCl) is the solute in a solution of saline water.}}

{{term|solution}}{{anchor|solutions}} {{defn|A homogeneous {{gli|mixture}} made up of multiple substances generally referred to as {{gli|solutes}} and {{gli|solvents}}.}}

{{term|solvated electron}} {{defn|}}

{{term|solvation}}{{anchor|solvate|solvates|solvated}} {{defn|Any stabilizing interaction of a {{gli|solute}} with a {{gli|solvent}}, or a similar interaction between a solvent and groups of an insoluble material (e.g. the ionic groups of an ion-exchange resin). Such interactions generally involve electrostatic forces and {{gli|van der Waals forces}}, as well as compound-specific effects such as {{gli|hydrogen bonding}}.<ref name="Gold Book"/> See also ''{{gli|dissolution}}''.}}

{{term|solvent}}{{anchor|solvents}} {{defn|The part of a {{gli|solution}} that dissolves the {{gli|solute}}. For example, water (H2O) is the solvent in a solution of saline water.}}

{{term|sonication}}{{anchor|sonicate|sonicates|sonicating|sonicated}} {{ghat|Also '''ultrasonication'''.}} {{defn|The process of irradiating a substance with sound energy, usually at ultrasound (>20 kHz) frequencies, in order to agitate the particles in a sample for various purposes, such as increasing the {{gli|reaction rate|rate}} of a chemical reaction or preparing vesicles in mixtures of surfactants and water.<ref name="Gold Book"/>}}

{{term|spatial isomer}} {{defn|See ''{{gli|stereoisomer}}''.}}

{{term|content=specific heat capacity ({{mvar|''c''p}})}} {{ghat|Also '''massic heat capacity'''.}} {{defn|The {{gli|heat capacity}} of a sample of a substance divided by the {{gli|mass}} of the sample. Informally, it is the amount of {{gli|heat}} that must be added to one unit of mass of the substance in order to cause an increase of one unit in {{gli|temperature}}. The {{gli|SI}} unit of specific heat capacity is {{gli|joule}} per {{gli|kelvin}} per {{gli|kilogram}} (J/K/kg). Specific heat capacity often varies with temperature and with each {{gli|state of matter}}.}}

{{term|spectrometry}} {{defn|See ''{{gli|mass spectrometry}}''.}}

{{term|spectroscopy}} {{defn|The study of {{gli|radiation}} and {{gli|matter}}, such as {{gli|X-ray}} absorption and emission spectroscopy.}}

{{term|standard conditions of temperature and pressure (STP)}} {{defn|A standardisation of ambient {{gli|temperature}} and {{gli|pressure}} used in order to easily compare experimental results. Standard temperature is 25 degrees Celsius (°C) and standard pressure is 100.000 kilopascals (kPa). Standard conditions are often denoted with the abbreviation ''STP'' or ''SATP''.}}

{{term|state of matter}}{{anchor|states of matter|state|states}} {{defn|The condition of {{gli|matter}} existing in a distinct, homogeneous, macroscopic form. {{gli|solid|Solid}}, {{gli|liquid}}, {{gli|gas}}, and {{gli|plasma}} are the four traditional states of matter and the most well-known. See also ''{{gli|phase}}''.}}

{{term|stereogenic center}}{{anchor|stereogenic centers|stereocenter|stereocenters}} {{ghat|Also '''stereocenter'''.}} {{defn|}}

{{term|stereoisomer}}{{anchor|stereoisomers}} {{ghat|Also '''spatial isomer'''.}} {{defn|An {{gli|isomer}} which possesses an identical {{gli|chemical composition}} but which differs in the spatial arrangement of its atoms.}}

{{term|stoichiometry}}{{anchor|stoichiometric}} {{defn|The calculation of quantities of {{gli|reactants}} and {{gli|products}} in {{gli|chemical reactions}}. Stoichiometry is based on the {{gli|law of conservation of mass}} and the observation that quantities of reactants and products typically exist in ratios of positive integers, implying that if the amounts of the separate reactants are known, then the amounts of the products can be calculated, and vice versa.}}

{{term|strong acid}}{{anchor|strong acids}} {{defn|An {{gli|acid}} that completely {{gli|dissociates}} in solution according to the reaction <chem>HA + S <=> SH+ + A-</chem>, or to such an extent that the {{gli|concentration}} of the undissociated species <chem>HA</chem> is too low to be measured. Any acid with a {{gli|acid dissociation constant|pKa}} of less than approximately -2 is generally considered a strong acid; an example is hydrochloric acid (HCl). Contrast ''{{gli|weak acid}}''.}}

{{term|structural formula}}{{anchor|structural formulas}} {{defn|A graphical representation of the molecular structure and geometry of a particular {{gli|chemical compound}}, showing how the {{gli|atoms}} are arranged in real, three-dimensional space. {{gli|bond|Chemical bonding}} within the molecule is also shown, either implicitly or explicitly. When known with certainty, structural formulas are very useful because they allow chemists to visualize the molecules and the structural changes that occur in them during {{gli|chemical reactions}}.}}

{{term|subatomic particle}}{{anchor|subatomic particles}} {{defn|Any particle that is smaller than an {{gli|atom}}. Examples include {{gli|protons}}, {{gli|neutrons}}, and {{gli|electrons}}.}}

{{term|sublimation}}{{anchor|sublimate|sublimates|sublimating|sublimated}} {{defn|The {{gli|phase transition}} of a substance from a {{gli|solid}} to a limewater fuel or {{gli|gas}} without an apparent intervening transition to a {{gli|liquid}} in the process.}}

{{term|substance}} {{defn|See ''{{gli|chemical substance}}''.}}

{{term|substituent}}{{anchor|substituents}} {{defn|An {{gli|atom}} or a group of atoms which substitutes or replaces another atom or group of atoms within a larger {{gli|molecule}} as the {{gli|product}} of a {{gli|chemical reaction}}, thereby becoming a {{gli|moiety}} of the newly formed compound, generally without causing any significant change to other parts of the same molecule. For example, a {{gli|hydroxyl group}} may be substituted for any of the hydrogen atoms in {{gli|benzene}} to form {{gli|phenol}}. See also ''{{gli|side chain}}'' and ''{{gli|functional group}}''.}}

{{term|substitution reaction}}{{anchor|substitution|substitutions|substitute|substitutes|substituting|substituted}} {{defn|A type of {{gli|chemical reaction}} in which one {{gli|functional group}} or {{gli|substituent}} within a larger compound replaces or is substituted for another functional group or substituent.}}

{{term|superheavy elements}} {{defn|See ''{{gli|transactinides}}''.}}

{{term|surfactant}}{{anchor|surfactants}} {{defn|A substance which lowers the {{gli|surface tension}} of the medium in which it is {{gli|dissolved}}, and/or the interfacial tension with other phases, and, accordingly, is positively {{gli|adsorbed}} at the liquid–vapor and/or other interfaces.<ref name="Gold Book"/>}}

{{term|suspension}}{{anchor|suspensions|suspended}} {{defn|A heterogeneous {{gli|mixture}} that contains {{gli|solid}} particles which are sufficiently large for sedimentation to occur, by which such particles separate from and settle out of the fluid over time if left undisturbed. In a suspension, the {{gli|solute}} does not {{gli|dissolve}} but remains {{gli|dispersed}} or suspended throughout the fluid {{gli|solvent}} only transiently and with mechanical agitation. Contrast ''{{gli|colloid}}'' and ''{{gli|solution}}''.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== T == {{glossary}} {{term|tarnish}} {{defn|A thin layer of {{gli|corrosion}} that forms on the surface of copper, brass, aluminum, magnesium, and other soft {{gli|metals}} or {{gli|alloys}} as their outermost layer undergoes a chemical reaction with the surrounding air, often but not necessarily involving atmospheric oxygen. Tarnish usually appears as a dull grey, black, or sometimes iridescent film or coating on the metal. It is a self-limiting surface phenomenon, as the tarnished top layers of the metal protect underlying layers from reacting.}}

{{term|temperature}} {{defn|A proportional measure of the average {{gli|kinetic energy}} of the random motions of the constituent microscopic particles of a system. The {{gli|SI}} unit for temperature is the {{gli|kelvin}}.}}

{{term|ternary compound}} {{defn|A chemical {{gli|compound}} containing three different {{gli|elements}}.<ref name="Daintith"/>}}

{{term|terpene}} {{defn|A class of naturally occurring {{gli|unsaturated}} {{gli|hydrocarbons}} with carbon skeletons derived from one or more units of isoprene ({{chem|C|5|H|8}}). Terpenes are often subclassified according to the total number of carbon atoms they contain, e.g. the {{chem|C|5}} hemiterpenes, {{chem|C|10}} monoterpenes, {{chem|C|20}} diterpenes, etc.}}

{{term|theoretical yield}} {{defn|See ''{{gli|yield}}''.}}

{{term|thermal conductivity}} {{defn|The property of a material that allows it to conduct thermal energy or {{gli|heat}} (a quantity often denoted by <math>k</math>).}}

{{term|thermochemistry}} {{defn|The study of the absorption or release of {{gli|heat}} during a {{gli|chemical reaction}}.}}

{{term|thermodynamic stability}} {{defn|The condition of a system being in its lowest energy state with its environment (equilibrium).}}

{{term|thermodynamics}} {{defn|The study of the effects of changing temperature, volume, or pressure (or work, heat, and energy) on a macroscopic scale.}}

{{term|thermometer}} {{defn|An instrument used to measure {{gli|temperature}}.}}

{{term|thiol}}{{anchor|thiols}} {{defn|no=1|Any of a class of {{gli|organosulfur compounds}} consisting of a sulfur atom attached to a hydrogen atom and any other organic {{gli|substituent}}, with the general formula R–SH. Thiols are the sulfur analogues of {{gli|alcohols}}. Also '''''thiol derivative''''' and '''''mercaptan'''''.}} {{defn|no=2|The –SH {{gli|functional group}} itself. Also '''''sulfhydryl''''', '''''sulfanyl''''', and '''''mercapto'''''.}} thumb|right|350px|The skeletal formula for a generic '''{{gli|thiol}}''', where R denotes a variable carbon-containing substituent group

{{term|titration}}{{anchor|titrations}} {{ghat|Also '''titrimetry''' or '''volumetric analysis'''.}} {{defn|A laboratory method of quantitative chemical analysis that is used to determine the {{gli|concentration}} of an identified {{gli|analyte}}. The procedure involves preparing a particular {{gli|reagent}} as a {{gli|standard solution}} of known concentration and volume (called the ''titrant'' or ''titrator'') and allowing it to {{gli|chemical reaction|react}} with a solution of the analyte (called the ''titrand'') to determine the latter's concentration.}}

{{term|torr}}{{anchor|torrs}} {{defn|A unit for measuring {{gli|pressure}}, equivalent to 133.322 Pa or 1.3158 × 10−3 atm.}}

{{term|trace element}} {{defn|An {{gli|element}} in a sample which has an average {{gli|concentration}} of less than 100 parts per million atoms or less than 100 micrograms per gram.<ref name="McGraw-Hill"/>}}

{{term|transactinides}} {{ghat|Also '''superheavy elements'''.}} {{defn|In the {{gli|periodic table}}, the set of {{gli|chemical elements}} with an {{gli|atomic number}} greater than 103, i.e. those heavier than the {{gli|actinides}}. The transactinides are a subset of the {{gli|transuranic elements}}.}}

{{term|transition metal}}{{anchor|transition metals}} {{defn|An {{gli|element}} whose atoms naturally occur with incompletely filled "d" sub-shells. These elements are grouped as the so-called ''{{gli|d-block|d-block elements}}'' in the {{gli|periodic table}}.}}

{{term|transuranic elements}} {{ghat|Also '''transuranium elements'''.}} {{defn|The set of {{gli|chemical elements}} with an {{gli|atomic number}} greater than 92, i.e. occurring after uranium in the {{gli|periodic table}}. None of the transuranic elements are stable in naturally occurring conditions.}}

{{term|triple bond}}{{anchor|triple bonds|triple-bonded}} {{defn|A {{gli|bond}} that involves the {{gli|covalent}} sharing of three {{gli|electron pair|pairs of electrons}} (for example, the diatomic nitrogen molecule, N2, is composed of two nitrogen atoms linked by a triple bond).}}

{{term|triple point}} {{defn|The place where {{gli|temperature}} and {{gli|pressure}} of three {{gli|phases}} are the same. Water has a special phase diagram.}} thumb|right|350px|A phase diagram showing the '''{{gli|triple point}}''' and {{gli|critical point}} of a substance

{{term|Tyndall effect}} {{defn|The effect of light scattering by {{gli|colloidal}} or {{gli|suspended}} particles.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== U == {{glossary}} {{term|UN number}} {{defn|A four-digit code used to note hazardous and flammable substances.}}

{{term|uncertainty}} {{defn|The notion that any measurement that involves estimation of any amount cannot be exactly reproducible.}}

{{term|uncertainty principle}} {{defn|Knowing the location of a particle makes the momentum uncertain, while knowing the momentum of a particle makes the location uncertain.}}

{{term|unit cell}} {{defn|The smallest repeating unit of a crystalline {{gli|lattice}}.}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== V == {{glossary}} {{term|vacuum flask}} {{ghat|Also '''Dewar flask''' or '''thermos'''.}} {{defn|A storage vessel consisting of two {{gli|flasks}} or other containers, placed one within the other and joined at the neck, and a space in between that is partially evacuated of air, creating a near-vacuum that significantly reduces the transfer of {{gli|heat}} between the vessel's interior and its ambient environment. Vacuum flasks can greatly lengthen the time over which their contents remain warmer or cooler than the ambient environment.}}

{{term|valence electron}}{{anchor|valence electrons}} {{defn|Any of the outermost {{gli|electrons}} of an atom, which are located in {{gli|electron shells}}.}}

{{term|valence bond theory}} {{defn|A theory explaining the chemical bonding within molecules by discussing valencies, the number of chemical bonds formed by an atom.}}

{{term|van der Waals force}}{{anchor|van der Waals forces}} {{defn|One of the forces (attraction/repulsion) between molecules.}}

{{term|van 't Hoff factor}} {{defn|The ratio of {{gli|moles}} of particles in {{gli|solution}} to moles of {{gli|solute}} dissolved.}}

{{term|vapor}} {{defn|When a substance is below the critical temperature while in the {{gli|gas}} phase.}}

{{term|vapor pressure}} {{ghat|Also '''equilibrium vapor pressure'''.}} {{defn|The {{gli|pressure}} exerted by a {{gli|vapor}} which is in thermodynamic equilibrium with its condensed phases ({{gli|solid}} or {{gli|liquid}}) at a given temperature in a {{gli|closed system}}. It is commonly described as the tendency of particles to spontaneously escape from the liquid or solid state into the gaseous state and is used as an indication of a liquid's {{gli|evaporation}} rate.}}

{{term|vaporization}}{{anchor|vaporize|vaporizes|vaporizing|vaporized|boil|boils|boiling|boiled}} {{ghat|Also '''boiling'''.}} {{defn|The {{gli|phase transition}} of a substance from a {{gli|liquid}} to a {{gli|gas}}.}}

{{term|vaporization point}} {{defn|See ''{{gli|boiling point}}''.}}

{{term|viscosity}} {{defn|A measure of the resistance of a {{gli|liquid}} to flow.}}

{{term|volatility}}{{anchor|volatile}} {{defn|A material quality which describes how readily a substance {{gli|vaporizes}}. At a given temperature and pressure, a substance with high volatility is more likely to exist as a {{gli|gas}}, while a substance with low volatility is more likely to exist as a {{gli|liquid}} or {{gli|solid}}; equivalently, less volatile substances will more readily {{gli|condense}} from a gaseous state than highly volatile ones.}}

{{term|volt (V)}}{{anchor|volt|volts}} {{defn|A derived unit of electric potential, electric potential difference, and {{gli|electromotive force}}, defined as one {{gli|joule}} of {{gli|mechanical work|work}} per {{gli|coulomb}}.}}

{{term|volume}} {{defn|The quantity of three-dimensional space enclosed by a closed surface, or the space that a {{gli|substance}} (solid, liquid, gas, or plasma) or shape occupies or contains. The {{gli|SI}} unit for volume is the cubic metre (m3).}}

{{term|volumetric analysis}} {{defn|See ''{{gli|titration}}''.}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== W == {{glossary}} {{term|watch glass}} {{defn|A circular, concave piece of glass commonly used in chemistry laboratories as a working surface for various purposes, such as evaporating liquids, holding solids while they are being weighed, heating small amounts of a substance, or as a cover for a {{gli|beaker}}.}}

{{term|water}} {{defn|A {{gli|polar}} {{gli|inorganic compound}} with the chemical formula H2O that is a tasteless, odorless, and generally colorless {{gli|liquid}} at {{gli|standard temperature and pressure}}, though it also occurs naturally as a {{gli|solid}} and a {{gli|gas}} at the Earth's surface. It is the most abundant substance on Earth and therefore an integral component of virtually all chemical and biological systems. Water is often described as the "universal {{gli|solvent}}" for its inherent ability to {{gli|dissolve}} many substances.}}

{{term|water of crystallization}} {{ghat|Also '''water of hydration'''.}} {{defn|{{gli|water|Water}} molecules that are present inside {{gli|crystals}}. Upon {{gli|crystallization}} from water or {{gli|aqueous solutions}}, many compounds incorporate water in the interstices of their crystalline frameworks; the water molecules are typically present in a {{gli|stoichiometric}} ratio and may interact to varying degrees with the atoms of the crystal.}}

{{term|wave function}} {{defn|A mathematical function describing the position of an {{gli|electron}} within a three-dimensional space.}}

{{term|weak acid}} {{defn|An {{gli|acid}} that only partially {{gli|dissociates}} when dissolved in a {{gli|solvent}} because, according to the reaction <chem>HA <=> H+ + A-</chem>, {{gli|equilibrium}} is reached while the {{gli|concentration}} of the undissociated species <chem>HA</chem> is still significant; an example is acetic acid (CH3COOH). Contrast ''{{gli|strong acid}}''.}}

{{term|wet chemistry}} {{ghat|Also '''bench chemistry''' or '''classical chemistry'''.}} {{defn|A form of {{gli|analytical chemistry}} which uses classical laboratory methods such as simple observation and elementary chemical tests to study chemicals and chemical reactions, i.e. without the use of sophisticated instruments or automated or computerized analysis. It is often used in schools to teach the principles of chemistry to students.}}

{{term|work-up}} {{defn|The series of manipulations required to isolate and purify the desired {{gli|product}} or products of a {{gli|chemical reaction}}.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== X == {{glossary}} {{term|X-ray}} {{defn|A form of ionizing, electromagnetic radiation between gamma and ultraviolet rays in the {{gli|electromagnetic spectrum}}.}}

{{term|X-ray diffraction}} {{defn|A laboratory method for establishing the structure of a {{gli|crystalline}} solid by directing single wavelength X-rays at the solid and analyzing the resulting diffraction pattern.}}

{{term|X-ray photoelectron spectroscopy}} {{defn|A {{gli|spectroscopic}} technique used to measure the {{gli|chemical composition}} of a material.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== Y == {{glossary}} {{term|yield}} {{defn|The quantifiable amount of {{gli|product}} produced during a {{gli|chemical reaction}}.}} {{glossary end}}

== Z == {{glossary}} {{term|zero-point energy (ZPE)}}{{anchor|zero-point energy}} {{defn|}}

{{term|zone melting}} {{defn|Any of several methods of {{gli|purifying}} crystalline solids which involve applying heat to a small region of a larger solid (particularly a metal ingot) until localized {{gli|melting}} occurs, creating a molten zone which is then slowly moved along the surface to other parts of the solid by moving the target of the heating element. As it moves, the forward edge of the molten zone continuously melts new areas of impure solid, while leaving a path of purer solid behind it as previously melted areas are cooled and resolidified; because the molten {{gli|liquid}} phase can hold a higher {{gli|concentration}} of impurities than the {{gli|solid}} phase, the impurities of melted areas tend to concentrate in the molten zone and be carried along as it moves, leaving behind regions with fewer impurities. The process is commonly used in the refinement of high-purity {{gli|metalloids}} for use in {{gli|semiconductors}}.}}

{{term|zinc}} {{defn|A metallic {{gli|chemical element}} with {{gli|atomic number}} 30 and {{gli|atomic symbol|symbol}} Zn.}}

{{term|zwitterion}}{{anchor|zwitterions|zwitterionic}} {{ghat|Also '''inner salt''' and '''dipolar ion'''.}} {{defn|Any molecule that contains an internal {{gli|polarity}} by virtue of having an equal number of positively charged and negatively charged {{gli|functional groups}}.}} {{glossary end}}

{{Compact TOC|side=yes|center=yes|top=yes|num=yes|extlinks=yes|seealso=yes|refs=yes|nobreak=yes|}}

== References == {{reflist}}

== External links == *[https://web.archive.org/web/20100124150119/http://goldbook.iupac.org/index.html IUPAC Compendium of Chemical Terminology]

Category:Chemistry-related lists Category:Chemistry Chemistry Category:Risk Category:Safety Category:Wikipedia glossaries using description lists