Group 6 element

{{short description|Group of chemical elements}} {{for|the group VIA (CAS), also referred to as "Group 6"|Chalcogen}} {{Infobox periodic table group | title = Group 6 {{nowrap|in the periodic table}} | group number= 6 | trivial name= | by element = chromium group | CAS = VIB | old IUPAC = VIA | mark = Cr,Mo,W,Sg | left = group 5 | right = group 7 }} {| class="floatright" ! colspan=2 style="text-align:left;" | ↓ Period |- ! 4 | {{element cell image|24|Chromium|Cr| |Solid|Transition metal|Primordial|image=Chromium crystals and 1cm3 cube.jpg|image caption=Chromium crystal bar}} |- ! 5 | {{element cell image|42|Molybdenum |Mo| |Solid|Transition metal|Primordial|image=Molybdenum crystaline fragment and 1cm3 cube.jpg|image caption=Molybdenum crystal bar}} |- ! 6 | {{element cell image|74|Tungsten |W| |Solid|Transition metal|Primordial|image=Wolfram evaporated crystals and 1cm3 cube.jpg|image caption=Tungsten crystal bar}} |- ! 7 | {{element cell image|106|Seaborgium|Sg| |Unknown phase|Transition metal|Synthetic}} |- | colspan="2"| ---- ''Legend'' {| style="text-align:center; border:0; margin: 0 auto" |- | style="border:{{element color|Primordial}}; background:{{Element color|table mark}}; padding:0 2px;" | primordial element |- | style="border:{{element color|Synthetic}}; background:{{Element color|table mark}}; padding:0 2px;" | synthetic element |} |}

'''Group 6''', numbered by IUPAC style, is a group of elements in the periodic table. Its members are chromium (Cr), molybdenum (Mo), tungsten (W), and seaborgium (Sg). These are all transition metals and chromium, molybdenum and tungsten are refractory metals.

The electron configuration of these elements do not follow a unified trend, though the outermost shells do correlate with trends in chemical behavior:

{| class="wikitable" style="white-space:nowrap;" |- !''Z'' !! Element !! Electrons per shell |- | 24 || chromium || 2, 8, 13, 1 |- | 42 || molybdenum || 2, 8, 18, 13, 1 |- | 74 || tungsten || 2, 8, 18, 32, 12, 2 |- | 106 || seaborgium || 2, 8, 18, 32, 32, 12, 2 |}

"Group 6" is the new IUPAC name for this group; the old style name was "''group VIB''" in the old US system (CAS) or "''group VIA''" in the European system (old IUPAC). Group 6 must not be confused with the group with the old-style group crossed names of either ''VIA'' (US system, CAS) or ''VIB'' (European system, old IUPAC). ''That'' group is now called group 16.

==History== [[File:Cut Ruby.jpg|left|thumb|upright|The red colour of rubies is from a small amount of chromium(III).]]

===Discoveries=== Chromium was first reported on July 26, 1761, when Johann Gottlob Lehmann found an orange-red mineral in the Beryozovskoye mines in the Ural Mountains of Russia, which he named "Siberian red lead," which was found out in less than 10 years to be a bright yellow pigment.<ref name="ChromiumVI"/> Though misidentified as a lead compound with selenium and iron components, the mineral was crocoite with a formula of PbCrO4.<ref name="ChromiumVI">{{cite book|title = Chromium (VI) Handbook|publisher = CRC Press|year = 2005|isbn = 978-1-56670-608-7|pages = 7–11|author1=Guertin, Jacques |author2=Jacobs, James Alan |author3=Avakian, Cynthia P. }}</ref> Studying the mineral in 1797, Louis Nicolas Vauquelin produced chromium trioxide by mixing crocoite with hydrochloric acid, and metallic chromium by heating the oxide in a charcoal oven a year later.<ref>{{cite journal|url = https://books.google.com/books?id=6dgPAAAAQAAJ|journal =Journal of Natural Philosophy, Chemistry, and the Arts|year = 1798|page = 146|volume =3|title = Memoir on a New Metallic Acid which exists in the Red Lead of Sibiria|first = Louis Nicolas|last = Vauquelin}}</ref> He was also able to detect traces of chromium in precious gemstones, such as ruby or emerald.<ref name="ChromiumVI"/><ref>{{Cite web|last = van der Krogt|first = Peter|title = Chromium|url = http://elements.vanderkrogt.net/element.php?sym=Cr|access-date = 2008-08-24}}</ref>

Molybdenite—the principal ore from which molybdenum is now extracted—was previously known as molybdena, which was confused with and often implemented as though it were graphite. Like graphite, molybdenite can be used to blacken a surface or as a solid lubricant.<ref name="Lansdown1999">{{cite book | last1 = Lansdown | first1 = A.R. | title = Molybdenum disulphide lubrication | volume = 35 | chapter = Tribology and Interface Engineering | publisher = Elsevier | year = 1999 | isbn = 978-0-444-50032-8}}</ref> Even when molybdena was distinguishable from graphite, it was still confused with a galena (a common lead ore), which took its name from Ancient Greek {{lang|grc|Μόλυβδος}} ''{{lang|grc-Latn|molybdos}}'', meaning ''lead''.<ref name="nbb">{{cite book|last = Emsley|first = John|title = Nature's Building Blocks|url=https://books.google.com/books?id=j-Xu07p3cKwC&pg=PA265|publisher = Oxford University Press|year= 2001|location = Oxford|pages = 262–266|isbn =0-19-850341-5}}</ref> It was not until 1778 that Swedish chemist Carl Wilhelm Scheele realized that molybdena was neither graphite nor lead.<ref name="elemental">{{cite web|last = Gagnon|first = Steve|title = Molybdenum|publisher = Jefferson Science Associates, LLC|url = http://education.jlab.org/itselemental/ele042.html|access-date = 2007-05-06}}</ref><ref>{{cite journal|author = Scheele, C. W. K.|title = Versuche mit Wasserbley;Molybdaena|journal = Svenska Vetensk. Academ. Handlingar|page=238|year = 1779|volume = 40|url = http://resolver.sub.uni-goettingen.de/purl?PPN324352840_0040}}</ref> He and other chemists then correctly assumed that it was the ore of a distinct new element, named ''molybdenum'' for the mineral in which it was discovered. Peter Jacob Hjelm successfully isolated molybdenum by using carbon and linseed oil in 1781.<ref name="nbb" /><ref>{{cite journal|author = Hjelm, P. J.|title = Versuche mit Molybdäna, und Reduction der selben Erde|journal = Svenska Vetensk. Academ. Handlingar|page = 268|year = 1788|volume = 49|url = http://resolver.sub.uni-goettingen.de/purl?PPN324352840_0009_02_NS}}</ref>

Regarding tungsten, in 1781 Carl Wilhelm Scheele discovered that a new acid, tungstic acid, could be made from scheelite (at the time named tungsten). Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid.<ref name="SaundersN">{{cite book|last=Saunders|first=Nigel|title=Tungsten and the Elements of Groups 3 to 7 (The Periodic Table)|publisher=Heinemann Library|location=Chicago, Illinois|date=February 2004|isbn=1-4034-3518-9|url-access=registration|url=https://archive.org/details/tungstenelements00nige}}</ref> In 1783, José and Fausto Elhuyar found an acid made from wolframite that was identical to tungstic acid. Later that year, in Spain, the brothers succeeded in isolating tungsten by reduction of this acid with charcoal, and they are credited with the discovery of the element.<ref name="ITIAnews_0605">{{cite news|url=http://www.itia.info/FileLib/Newsletter_2005_06.pdf|title=ITIA Newsletter|date=June 2005|publisher=International Tungsten Industry Association|access-date=2008-06-18|archive-url=https://web.archive.org/web/20110721214335/http://www.itia.info/FileLib/Newsletter_2005_06.pdf|archive-date=2011-07-21}}</ref><ref name="ITIAnews_1205">{{cite news|url=http://www.itia.info/FileLib/Newsletter_2005_12.pdf|title=ITIA Newsletter|date=December 2005|publisher=International Tungsten Industry Association|access-date=2008-06-18|archive-url=https://web.archive.org/web/20110721214335/http://www.itia.info/FileLib/Newsletter_2005_12.pdf|archive-date=2011-07-21}}</ref>

Seaborgium was first produced by a team of scientists led by Albert Ghiorso who worked at the Lawrence Berkeley Laboratory in Berkeley, California, in 1974. They created seaborgium by bombarding atoms of californium-249 with ions of oxygen-18 until seaborgium-263 was produced.

===Historical development and uses=== During the 1800s, chromium was primarily used as a component of paints and in tanning salts. At first, crocoite from Russia was the main source, but in 1827, a larger chromite deposit was discovered near Baltimore, United States. This made the United States the largest producer of chromium products until 1848 when large deposits of chromite where found near Bursa, Turkey.<ref name="NRC">{{cite book|title = Chromium|author = National Research Council (U.S.). Committee on Biologic Effects of Atmospheric Pollutants|publisher = National Academy of Sciences|year = 1974 |isbn = 978-0-309-02217-0 |url = https://books.google.com/books?id=ZZsrAAAAYAAJ|page = 155}}</ref> Chromium was used for electroplating as early as 1848, but this use only became widespread with the development of an improved process in 1924.<ref name="Crplating">{{cite book|title = Nickel and Chromium Plating| publisher = Woodhead Publishing|year = 1993| isbn = 978-1-85573-081-6| pages = 9–12|chapter = History of Chromium Plating|author1=Dennis, J. K. |author2=Such, T. E. }}</ref>

For about a century after its isolation, molybdenum had no industrial use, owing to its relative scarcity, difficulty extracting the pure metal, and the immaturity of the metallurgical subfield.<ref name="Hoyt1921">{{cite book | last1 = Hoyt | first1 = Samuel Leslie | title = Metallography, Volume 2 | publisher = McGraw-Hill | year = 1921 }}</ref><ref name="Krupp1888">{{cite book | last1 = Krupp | first1 = Alfred | last2 = Wildberger | first2 = Andreas | title = The metallic alloys: A practical guide for the manufacture of all kinds of alloys, amalgams, and solders, used by metal-workers ... with an appendix on the coloring of alloys | publisher = H.C. Baird & Co. | year = 1888 | page = 60 }}</ref><ref name='Gupta1992'>{{cite book | last1 = Gupta | first1 = C.K. | title = Extractive Metallurgy of Molybdenum | publisher = CRC Press | year = 1992 | isbn = 978-0-8493-4758-0}}</ref> Early molybdenum steel alloys showed great promise in their increased hardness, but efforts were hampered by inconsistent results and a tendency toward brittleness and recrystallization. In 1906, William D. Coolidge filed a patent for rendering molybdenum ductile, leading to its use as a heating element for high-temperature furnaces and as a support for tungsten-filament light bulbs; oxide formation and degradation require that moly be physically sealed or held in an inert gas. In 1913, Frank E. Elmore developed a flotation process to recover molybdenite from ores; flotation remains the primary isolation process. During the first World War, demand for molybdenum spiked; it was used both in armor plating and as a substitute for tungsten in high-speed steels. Some British tanks were protected by 75 mm (3 in) manganese steel plating, but this proved to be ineffective. The manganese steel plates were replaced with 25 mm (1 in) molybdenum-steel plating allowing for higher speed, greater maneuverability, and better protection.<ref name="nbb" /> After the war, demand plummeted until metallurgical advances allowed extensive development of peacetime applications. In World War II, molybdenum again saw strategic importance as a substitute for tungsten in steel alloys.<ref name="Millholland1941">{{cite news | first = Ray | last = Millholland | title = Battle of the Billions: American industry mobilizes machines, materials, and men for a job as big as digging 40 Panama Canals in one year | date = August 1941 | work = Popular Science | page = 61 }}</ref>

In World War II, tungsten played a significant role in background political dealings. Portugal, as the main European source of the element, was put under pressure from both sides, because of its deposits of wolframite ore at Panasqueira. Tungsten's resistance to high temperatures and its strengthening of alloys made it an important raw material for the arms industry.<ref name="portugal">{{cite journal|last=Stevens|first=Donald G.|year=1999|title=World War II Economic Warfare: The United States, Britain, and Portuguese Wolfram|journal=The Historian|volume=61|issue=3|pages=539–556|doi=10.1111/j.1540-6563.1999.tb01036.x}}</ref>

==Chemistry== Unlike other groups, the members of this family do not show patterns in its electron configuration, as two lighter members of the group are exceptions from the Aufbau principle: {| class="wikitable" |- !Z !! Element !! Numerical Bohr model |- | 24 || chromium || 2, 8, 13, 1 |- | 42 || molybdenum || 2, 8, 18, 13, 1 |- | 74 || tungsten || 2, 8, 18, 32, 12, 2 |- | 106 || seaborgium || 2, 8, 18, 32, 32, 12, 2 |}

Most of the chemistry has been observed only for the first three members of the group. The chemistry of seaborgium is not very established and therefore the rest of the section deals only with its upper neighbors in the periodic table. The elements in the group, like those of groups 7–11, have high melting points, and form volatile compounds in higher oxidation states. All the elements of the group are relatively nonreactive metals with a high melting points (1907 °C, 2477 °C, 3422 °C); that of tungsten is the highest of all metals. The metals form compounds in different oxidation states: chromium forms compounds in all states from −2 to +6:<ref name="Schmidt"/> disodium pentacarbonylchromate, disodium decacarbonyldichromate, bis(benzene)chromium, tripotassium pentanitrocyanochromate, chromium(II) chloride, chromium(III) oxide, chromium(IV) chloride, potassium tetraperoxochromate(V), and chromium(VI) dichloride dioxide; the same is also true for molybdenum and tungsten, but the stability of the +6 state grows down the group.<ref name="Schmidt">{{cite book|title=Anorganische Chemie II.|chapter = VI. Nebengruppe|pages=119–127|first = Max|last =Schmidt|publisher=Wissenschaftsverlag|year = 1968|language=de}}</ref> Depending on oxidation states, the compounds are basic, amphoteric, or acidic; the acidity grows with the oxidation state of the metal.

==Occurrence and production==

=== Chromium === Chromium is a very common naturally occurring element. It is the 21st most abundant element in the Earth's crust with an average concentration of 100 ppm. The most common oxidation states for chromium are zero, trivalent, and hexavalent states. Most naturally occurring chromium is in the hexavalent state.<ref>{{Cite journal |last=Barnhart |first=J. |date=August 1997 |title=Occurrences, uses, and properties of chromium |journal=Regulatory Toxicology and Pharmacology |volume=26 |issue=1 Pt 2 |pages=S3–7 |doi=10.1006/rtph.1997.1132 |issn=0273-2300 |pmid=9380835}}</ref> About two-fifths of the worlds chromium are produced in South Africa, with Kazakhstan, India, Russia, and Turkey following. Chromium is mined as chromite ore.

The two main products of chromium refinement are ferrochromium and chromium metal. Ferrochromium is obtained by reducing chromite ore with either aluminium or silicon at high temperatures.<ref name=":0">{{Cite book |last=Papp |first=John F. |url=https://books.google.com/books?id=zNicdkuulE4C&pg=PA309#v=onepage&q&f=false |title=Industrial Minerals & Rocks: Commodities, Markets, and Uses |last2=Lipin |first2=Bruce R. |date=2006 |publisher=SME |isbn=978-0-87335-233-8 |edition=7th |language=en |archive-url=https://web.archive.org/web/20240610050310/https://books.google.com/books?id=zNicdkuulE4C&pg=PA309#v=onepage&q&f=false |archive-date=2024-06-10}}</ref> For chromium metal, the iron must be separated first using a two-step roasting and leaching process. By heating with sodium and calcium carbonates in air, the chromium is oxidised to its hexavalent form, while the iron forms stable Fe2O3. The insoluble iron oxide is removed in the subsequent leaching process, and the resulting chromium can be isolated by reaction with sulfuric acid (to form the dichromate), reduction with carbon (to form Cr2O3), and finally reduction with aluminium.<ref name=":0" />

=== Molybdenum === Molybdenum is the 54th most abundant element in the Earth's crust, and 42nd most abundant in the Universe.<ref>{{Cite book |last=Emsley |first=John |title=Nature's building blocks: an A - Z guide to the elements |date=2002 |publisher=Oxford University Press |isbn=978-0-19-850341-5 |edition=Repr. (with corr.) |location=Oxford}}</ref><ref>{{Cite book |title=Van Nostrand's Encyclopedia of Chemistry |publisher=Wiley-Interscience |year=1984 |isbn=978-0-471-61525-5 |editor-last=Considine |editor-first=Glenn D. |edition=5 |location=Hoboken, NJ |pages=1038–1040}}</ref> It is refined mainly from molybdenite, but is also present in wulfenite (PbMoO4) and powellite (CaMoO4). It is both mined as a principal ore and is also recovered as a byproduct of copper and tungsten mining.<ref>{{Cite book |title=CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data |date=1993 |publisher=CRC Press |isbn=978-0-8493-0474-3 |editor-last=Lide |editor-first=David R. |edition=74. ed., 1993-1994 |location=Boca Raton, Fla. |editor-last2=Chemical Rubber Company}}</ref> It is mainly mined in the United States, China, Chile, and Peru, with the total amount produced being 200,000 tonnes per year.<ref>{{Cite web |title=Molybdenum - Element information, properties and uses {{!}} Periodic Table |url=https://www.rsc.org/periodic-table/element/42/molybdenum |access-date=2023-09-22 |website=www.rsc.org}}</ref>

The processing of molybdenite involves roasting in air at 700 °C to produce MoO3, which is then usually extracted with aqueous ammonia to give ammonium molybdate. Copper impurities are then removed by treatment with hydrogen sulfide.<ref>{{Cite book |last=Holleman |first=Arnold F. |title=Lehrbuch der anorganischen Chemie |last2=Nils |first2=Wiberg |date=2019 |publisher=De Gruyter |isbn=978-3-11-007511-3 |editor-last=Wiberg |editor-first=Egon |edition=91.–100. Aufl. Reprint 2019 |location=Berlin Boston}}</ref> Ammonium molybdate converts to ammonium dimolybdate, which is isolated as a solid and heated to produce molybdenum trioxide.<ref>{{Cite book |title=Ullmann's encyclopedia of industrial chemistry |date=2010 |publisher=Wiley-VCH |isbn=978-3-527-30673-2 |location=Weinheim}}</ref> Reduction of this oxide with hydrogen affords molybdenum metal.<ref>{{Cite book |last=Gupta |first=C. K. |title=Extractive metallurgy of molybdenum |date=1992 |publisher=CRC Press |isbn=978-0-8493-4758-0 |location=Boca Raton}}</ref>

=== Tungsten === Tungsten is slightly more abundant in the Earth's crust than molybdenum, with an average concentration of 1.25 ppm.<ref>"Abundance of Elements in the Earth's Crust and in the Sea", ''CRC Handbook of Chemistry and Physics,'' 97th edition (2016–2017), sec. 14, pg. 17</ref> It is mainly found in the minerals wolframite and scheelite, and it usually never occurs as a free element in nature.<ref>"Tungsten, W, atomic number 74". ''Institute of rare earths elements and strategic metals.'' </ref> The largest producers of tungsten in the world are China (1,800,000 t), Canada (290,000 t), Russia (160,000 t), Vietnam (95,000 t) and Bolivia.<ref>{{Cite web |title=Tungsten Statistics and Information {{!}} U.S. Geological Survey |url=https://www.usgs.gov/centers/national-minerals-information-center/tungsten-statistics-and-information |access-date=2025-12-22 |website=www.usgs.gov |language=en}}</ref>

Tungsten is extracted from its ore through a multi-step process, resulting in WO3. This is then reduced with hydrogen or carbon to produce powdered tungsten.<ref>{{Cite book |last=Saunders |first=N. |title=Tungsten and the elements of Groups 3 to 7 |date=2003 |publisher=Heinemann Library |isbn=978-1-4034-0876-1 |series=The periodic table |location=Chicago, Ill}}</ref> Due to tungsten's very high melting point, it is often sintered with another metal, such as nickel, to produce an alloy with a lower melting point.<ref>{{Cite journal |last=Samsonov |first=G. V. |last2=Yakovlev |first2=V. I. |date=1967-08-01 |title=Activated sintering of tungsten with nickel additions |url=https://doi.org/10.1007/BF00774544 |journal=Soviet Powder Metallurgy and Metal Ceramics |language=en |volume=6 |issue=8 |pages=606–611 |doi=10.1007/BF00774544 |issn=1573-9066 |archive-url=https://rdcu.be/eVRxC |archive-date=December 22, 2025 |via=Springer|url-access=subscription }}</ref>

=== Seaborgium === Seaborgium is a synthetic transuranium element that does not occur in nature. The seaborgium-260 isotope can be made by bombarding lead-207 or -208 with chromium-54 nuclei;<ref>{{Cite journal |last=Barber |first=Robert C. |last2=Greenwood |first2=N. N. |last3=Hrynkiewicz |first3=A. Z. |last4=Jeannin |first4=Y. P. |last5=Lefort |first5=M. |last6=Sakai |first6=M. |last7=Ulehla |first7=I. |last8=Wapstra |first8=A. H. |last9=Wilkinson |first9=D. H. |date=1993-01-01 |title=Discovery of the transfermium elements. Part II: Introduction to discovery profiles. Part III: Discovery profiles of the transfermium elements (Note: For Part I see Pure Appl. Chem., Vol. 63, No. 6, pp. 879-886, 1991) |url=https://www.degruyter.com/document/doi/10.1351/pac199365081757/html |journal=Pure and Applied Chemistry |language=en |volume=65 |issue=8 |pages=1757–1814 |doi=10.1351/pac199365081757 |issn=1365-3075}}</ref> seaborgium-263 by bombarding californium-249 with oxygen-18 nuclei;<ref>{{Cite web |title=Seaborgium - Element information, properties and uses {{!}} Periodic Table |url=https://www.rsc.org/periodic-table/element/106/seaborgium |access-date=2023-09-22 |website=www.rsc.org}}</ref> and seaborgium-267 by bombarding hassium-271 with α-particles,<ref>{{Cite journal |last=Oganessian |first=Yu. Ts. |last2=Utyonkov |first2=V. K. |last3=Shumeiko |first3=M. V. |last4=Abdullin |first4=F. Sh. |last5=Adamian |first5=G. G. |last6=Dmitriev |first6=S. N. |last7=Ibadullayev |first7=D. |last8=Itkis |first8=M. G. |last9=Kovrizhnykh |first9=N. D. |last10=Kuznetsov |first10=D. A. |last11=Petrushkin |first11=O. V. |last12=Podshibiakin |first12=A. V. |last13=Polyakov |first13=A. N. |last14=Popeko |first14=A. G. |last15=Rogov |first15=I. S. |date=2024-05-06 |title=Synthesis and decay properties of isotopes of element 110: Ds 273 and Ds 275 |url=https://link.aps.org/doi/10.1103/PhysRevC.109.054307 |journal=Physical Review C |language=en |volume=109 |issue=5 |doi=10.1103/PhysRevC.109.054307 |issn=2469-9985|url-access=subscription }}</ref> among others.

==Precautions== While trivalent chromium compounds and chromium metal are insoluble, and are not considered a health hazard, hexavalent chromium compounds are genotoxic carcinogens.<ref>{{cite journal|pmid=22192535|pmc=4138963|year=2012|last1=Wise|first1=SS |title=Chromium and genomic stability |journal=Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis|volume=733|issue=1–2|pages=78–82|last2=Wise|first2=JP Sr|doi=10.1016/j.mrfmmm.2011.12.002|bibcode=2012MRFMM.733...78W }}</ref><ref>{{Cite journal |last=Barceloux |first=Donald G. |last2=Barceloux |first2=Donald |date=1999 |title=Chromium |url=http://www.tandfonline.com/doi/full/10.1081/CLT-100102418 |journal=Journal of Toxicology: Clinical Toxicology |language=en |volume=37 |issue=2 |pages=173–194 |doi=10.1081/CLT-100102418 |issn=0731-3810|url-access=subscription }}</ref> The acute oral toxicity of hexavalent chromium is 1.5-3.3 mg/kg,<ref>{{Cite journal |last=Katz |first=Sidney A. |last2=Salem |first2=Harry |date=1993 |title=The toxicology of chromium with respect to its chemical speciation: A review |url=https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/jat.2550130314 |journal=Journal of Applied Toxicology |language=en |volume=13 |issue=3 |pages=217–224 |doi=10.1002/jat.2550130314 |issn=0260-437X|url-access=subscription }}</ref> as it enters cells through similar transport mechanisms as sulfate and phosphate. Its strong oxidizing capability causes damage to the kidneys, liver, and red blood cells, resulting in liver and renal failure and hemolysis.<ref>{{Cite journal |last=Dayan |first=A D |last2=Paine |first2=A J |date=2001 |title=Mechanisms of chromium toxicity, carcinogenicity and allergenicity: Review of the literature from 1985 to 2000 |url=https://journals.sagepub.com/doi/10.1191/096032701682693062 |journal=Human & Experimental Toxicology |language=en |volume=20 |issue=9 |pages=439–451 |doi=10.1191/096032701682693062 |issn=0960-3271|url-access=subscription }}</ref> Chromate salts can also cause allergic reactions, leading to contact dermatitis, irritant dermatitis, and ulceration, sometimes known as "chrome ulcers".<ref>{{Cite web |date=2023-10-26 |title=Chrome contact allergy |url=https://dermnetnz.org/topics/chrome-allergy |access-date=2025-12-22 |website=DermNet® |language=en}}</ref><ref>{{Cite journal |last=Basketter |first=David |last2=Horev |first2=Liran |last3=Slodovnik |first3=Dany |last4=Merimes |first4=Sharon |last5=Trattner |first5=Akiva |last6=Ingber |first6=Arieh |date=2001 |title=Investigation of the threshold for allergic reactivity to chromium |url=https://onlinelibrary.wiley.com/doi/10.1034/j.1600-0536.2001.440202.x |journal=Contact Dermatitis |language=en |volume=44 |issue=2 |pages=70–74 |doi=10.1034/j.1600-0536.2001.440202.x |issn=0105-1873|url-access=subscription }}</ref>

Molybdenum is an essential element in most organisms, and an essential trace dietary element in humans.<ref>{{Citation |last=Schwarz |first=Guenter |title=Molybdenum in Human Health and Disease |date=2013 |work=Interrelations between Essential Metal Ions and Human Diseases |volume=13 |pages=415–450 |editor-last=Sigel |editor-first=Astrid |url=https://link.springer.com/10.1007/978-94-007-7500-8_13 |access-date=2025-12-22 |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/978-94-007-7500-8_13 |isbn=978-94-007-7499-5 |last2=Belaidi |first2=Abdel A. |editor2-last=Sigel |editor2-first=Helmut |editor3-last=Sigel |editor3-first=Roland K.O.|url-access=subscription }}</ref> However, long-term exposure to molybdenum dust and fumes can be toxic, causing irritation to the eyes and skin at low levels and fatigue, headaches, and joint pain at high levels.<ref>{{Cite web |date=2020-03-05 |title=Molybdenum (soluble) - IDLH {{!}} NIOSH {{!}} CDC |url=https://www.cdc.gov/niosh/idlh/moly-mo.html |access-date=2025-12-22 |website=www.cdc.gov |language=en-us}}</ref>

The risk of tungsten dust, particulates, and alloys in cancer and other adverse effects has been highlighted in vitro and in vivo,<ref>{{Cite journal |last=Laulicht |first=Freda |last2=Brocato |first2=Jason |last3=Cartularo |first3=Laura |last4=Vaughan |first4=Joshua |last5=Wu |first5=Feng |last6=Kluz |first6=Thomas |last7=Sun |first7=Hong |last8=Oksuz |first8=Betul Akgol |last9=Shen |first9=Steven |last10=Peana |first10=Massimiliano |last11=Medici |first11=Serenella |last12=Zoroddu |first12=Maria Antonietta |last13=Costa |first13=Max |date=2015 |title=Tungsten-induced carcinogenesis in human bronchial epithelial cells |url=https://linkinghub.elsevier.com/retrieve/pii/S0041008X15300284 |journal=Toxicology and Applied Pharmacology |language=en |volume=288 |issue=1 |pages=33–39 |doi=10.1016/j.taap.2015.07.003 |pmc=4579035 |pmid=26164860}}</ref><ref>{{Cite journal |last=Zoroddu |first=Maria A. |last2=Medici |first2=Serenella |last3=Peana |first3=Massimiliano |last4=Nurchi |first4=Valeria M. |last5=Lachowicz |first5=Joanna I. |last6=Laulicht-Glickc |first6=Freda |last7=Costa |first7=Max |date=2018-01-22 |title=Tungsten or Wolfram: Friend or Foe? |url=https://www.eurekaselect.com/151988/article |journal=Current Medicinal Chemistry |language=en |volume=25 |issue=1 |pages=65–74 |doi=10.2174/0929867324666170428105603|url-access=subscription }}</ref> though varies greatly depending on the animal and method of administration.<ref>{{Cite journal |last=Koutsospyros |first=A. |last2=Braida |first2=W. |last3=Christodoulatos |first3=C. |last4=Dermatas |first4=D. |last5=Strigul |first5=N. |date=2006 |title=A review of tungsten: From environmental obscurity to scrutiny |url=https://linkinghub.elsevier.com/retrieve/pii/S0304389405006928 |journal=Journal of Hazardous Materials |language=en |volume=136 |issue=1 |pages=1–19 |doi=10.1016/j.jhazmat.2005.11.007|url-access=subscription }}</ref><ref>{{Citation |last=Lagarde |first=Florence |title=Metabolism and Toxicity of Tungsten in Humans and Animals |date=2002-03-06 |work=Metals Ions in Biological System |volume=20024823 |editor-last=Sigel |editor-first=Astrid |url=http://www.crcnetbase.com/doi/abs/10.1201/9780203909331.ch22 |access-date=2025-12-22 |publisher=CRC Press |language=en |doi=10.1201/9780203909331.ch22 |isbn=978-0-8247-0765-1 |last2=Leroy |first2=Maurice |editor2-last=Sigel |editor2-first=Helmut|url-access=subscription }}</ref><ref>{{Cite journal |last=Marquet |first=P |last2=François |first2=B |last3=Lotfi |first3=H |last4=Turcant |first4=A |last5=Debord |first5=J |last6=Nedelec |first6=G |last7=Lachâtre |first7=G |date=1997-05-01 |title=Tungsten Determination in Biological Fluids, Hair and Nails by Plasma Emission Spectrometry in a Case of Severe Acute Intoxication in Man |url=https://dl.astm.org/jofs/article/42/3/527/25063/Tungsten-Determination-in-Biological-Fluids-Hair |journal=Journal of Forensic Sciences |language=en |volume=42 |issue=3 |pages=527–530 |doi=10.1520/JFS14162J |issn=0022-1198|url-access=subscription }}</ref> The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 5 mg/m3 over an 8-hour workday and a short term limit of 10 mg/m3.<ref>{{Cite web |title=CDC - NIOSH Pocket Guide to Chemical Hazards - Tungsten |url=https://www.cdc.gov/niosh/npg/npgd0645.html |access-date=2025-12-22 |website=www.cdc.gov}}</ref>

Seaborgium is a radioactive synthetic element that is not found in nature; the most stable known isotope has a half-life of approximately 14 minutes.

==Applications== * Alloys<ref>{{cite web|title=Molybdenum|publisher=AZoM.com Pty. Limited|year=2007|url=http://www.azom.com/details.asp?ArticleID=616|access-date=2007-05-06}}</ref> * Catalysts * High temperature and refractory applications, such as welding electrodes and kiln components. * Metallurgy, sometimes used in jet engines and gas turbines.<ref>{{cite web|title = Nickel-Based Superalloys|first = H. K. D. H.|last = Bhadeshia|url = http://www.msm.cam.ac.uk/phase-trans/2003/Superalloys/superalloys.html|access-date = 2009-02-17|publisher = University of Cambridge|archive-url = https://web.archive.org/web/20060825053006/http://www.msm.cam.ac.uk/phase-trans/2003/Superalloys/superalloys.html|archive-date = 2006-08-25}}</ref> * Dyes and pigments * Tanning * hard materials

==Biological occurrences== Group 6 is notable in that it contains some of the only elements in periods 5 and 6 with a known role in the biological chemistry of living organisms: molybdenum is common in enzymes of many organisms including humans, and tungsten has been identified in an analogous role in enzymes from some archaea, such as ''Pyrococcus furiosus''. In contrast, and unusually for a first-row d-block transition metal, chromium appears to have few biological roles, although it is thought to form part of the glucose metabolism enzyme in some mammals.

==References== {{Reflist}}

==See also== {{Periodic table (navbox)}} {{Navbox periodic table}} {{Group 6 elements}}

{{DEFAULTSORT:Group 06}} Category:Groups (periodic table)