# Halide
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{{Short description|Chemical compound composed of a halogen atom and some other element}}
{{otheruses}}
{{See also|Organic halide}}
{{refimprove|date=March 2018}}
Radii in picometers of common halogen atoms (gray/black) and the corresponding halide anions (blue)|right|thumb|120px
In [chemistry](/source/chemistry), a '''halide''' (rarely '''halogenide'''[{{Cite web|title=Definition of HALOGENIDE|url=https://www.merriam-webster.com/dictionary/halogenide|access-date=2022-01-07|website=www.merriam-webster.com|language=en}}]) is a [binary chemical compound](/source/Binary_phase), of which one part is a [halogen](/source/halogen) [atom](/source/atom) and the other part is an [element](/source/chemical_element) or [radical](/source/radical_(chemistry)) that is less [electronegative](/source/electronegative) (or more electropositive) than the halogen, to make a [fluoride](/source/fluoride), [chloride](/source/chloride), [bromide](/source/bromide), [iodide](/source/iodide), [astatide](/source/astatide), or theoretically [tennesside](/source/tennesside) compound. The [alkali metals](/source/alkali_metals) combine directly with halogens under appropriate conditions forming halides of the general formula, MX (X = F, Cl, Br or I). Many [salt](/source/salt_(chemistry))s are halides; the ''hal-'' syllable in ''halide'' and ''[halite](/source/halite)'' reflects [this correlation](/source/Halogen).[{{Greenwood&Earnshaw2nd| page = 82}}]
A '''halide ion''' is a halogen atom bearing a negative charge. The common halide [anion](/source/anion)s are [fluoride](/source/fluoride) ({{chem2|F-}}), [chloride](/source/chloride) ({{chem2|Cl-}}), [bromide](/source/bromide) ({{chem2|Br-}}), and [iodide](/source/iodide) ({{chem2|I-}}). Such ions are present in many [ionic](/source/ionic_bonding) halide salts. [Halide mineral](/source/Halide_mineral)s contain halides. All these halide anions are colorless. Halides also form covalent bonds, examples being colorless [TiF4](/source/titanium_tetrafluoride), colorless [TiCl4](/source/titanium_tetrachloride), orange [TiBr4](/source/titanium_tetrabromide), and brown [TiI4](/source/titanium_tetraiodide). The heavier members TiCl4, TiBr4, TiI4 can be distilled readily because they are molecular. The outlier is TiF4, [m.p. 284 °C](/source/melting_point), because it has a polymeric structure. Fluorides often differ from the heavier halides.[{{Greenwood&Earnshaw2nd| page = 694}}]
==Reactions==
===Redox===
Halides cannot be [reduced](/source/reduction_(chemistry)) under the usual laboratory conditions, but they all can be [oxidized](/source/Redox) to the parent halogens, which are [diatomic](/source/diatomic). Especially for iodide and less so for the lighter halides, intermediates can be observed and isolated. Best characterized is [triiodide](/source/triiodide). Many related species are known, including a host of [polyiodide](/source/polyiodide)s.
===Protonation===
Halides are conjugate bases of [hydrogen halide](/source/hydrogen_halide)s, which are all gases. When the protonation is conducted in aqueous solution, [hydrohalic acid](/source/hydrohalic_acid)s are produced.
===Reaction with silver ions===
Halide salts such as [{{chem2|KCl}}](/source/Potassium_chloride), [{{chem2|KBr}}](/source/Potassium_bromide) and [{{chem2|KI}}](/source/Potassium_iodide) are highly soluble in water to give colorless solutions. The solutions react readily with a solution of [silver nitrate](/source/silver_nitrate) {{chem2|AgNO3}}. These three halides form solid [precipitate](/source/precipitate)s:[{{Greenwood&Earnshaw2nd| page = 1184}}]
* [{{chem2|AgCl}}](/source/Silver_chloride): white
* [{{chem2|AgBr}}](/source/Silver_bromide): pale yellow
* [{{chem2|AgI}}](/source/Silver_iodide): yellow
Similar but slower reactions occur with [alkyl halide](/source/alkyl_halide)s in place of alkali metal halides, as described in the [Beilstein test](/source/Beilstein_test).
==Uses==
[Metal halides](/source/%3ACategory%3AMetal_halides) are used in [high-intensity discharge lamp](/source/high-intensity_discharge_lamp)s called [metal halide lamp](/source/metal_halide_lamp)s, such as those used in modern [street light](/source/street_light)s. These are more [energy-efficient](/source/Energy_conversion_efficiency) than [mercury-vapor lamp](/source/mercury-vapor_lamp)s, and have much better [colour rendition](/source/colour_rendition) than [orange](/source/orange_(colour)) [high-pressure sodium lamps](/source/Sodium-vapor_lamp). Metal halide lamps are also commonly used in [greenhouse](/source/greenhouse)s or in rainy climates to supplement natural [sunlight](/source/sunlight).
[Silver halide](/source/Silver_halide)s are used in [photographic film](/source/photographic_film)s and [papers](/source/photographic_paper). When the film is [developed](/source/photographic_processing), the silver halides which have been exposed to light are reduced to metallic silver, forming an image.
Halides are also used in [soldering flux](/source/Flux_(metallurgy)), commonly as a Cl or Br equivalent (e.g [ZnCl](/source/Zinc_chloride)).[{{Cite web |url=http://www.indium.com/halogen-free/assets/PDF/Indium8_9HF_Overview.pdf |title=Halogen-Free Solder Paste |access-date=2011-03-21 |archive-url=https://web.archive.org/web/20120317004413/http://www.indium.com/halogen-free/assets/PDF/Indium8_9HF_Overview.pdf |archive-date=2012-03-17 |url-status=dead }}]
Synthetic [organic chemistry](/source/organic_chemistry) often incorporates halogens into [organohalide](/source/organohalide) compounds.
==See also==
* [Salinity](/source/Salinity)
* [Organohalide](/source/Organohalide)
* [Hydrogen halide](/source/Hydrogen_halide)
* [Silver halide](/source/Silver_halide)
==References==
{{reflist}}
{{Authority control}}
Category:Salts
Category:Halides
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Adapted from the Wikipedia article [Halide](https://en.wikipedia.org/wiki/Halide) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Halide?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.