Group 9 element

Short description: Group of chemical elements

Template:Infobox periodic table group

↓ Period

4 |

Cobalt (Co)
27 Transition metal
5 |

Rhodium (Rh)
45 Transition metal
6 |

Iridium (Ir)
77 Transition metal
7 | Meitnerium (Mt)
109 unknown chemical properties

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Legend

| primordial element

synthetic element

Group 9, by modern IUPAC numbering,[1] is a group (column) of chemical elements in the d-block of the periodic table. Members of Group 9 include cobalt (Co), rhodium (Rh), iridium (Ir) and meitnerium (Mt).[2] These elements are among the rarest of the transition metals,[3] and as of 2025 rhodium and iridium are the only non-radioactive metals with higher prices per weight than gold.[4]

Like other groups, the members of this family show patterns in electron configuration, especially in the outermost shells, resulting in trends in chemical behavior; however, rhodium deviates from the pattern.

## Contents

* 1 History
* 1.1 Cobalt
* 1.2 Rhodium
* 1.3 Iridium
* 1.4 Meitnerium
* 2 Properties
* 3 Biological role
* 4 See also
* 5 Notes
* 6 References

## History

"Group 9" is the modern standard designation for this group, adopted by the IUPAC in 1990.[2] In the older group naming systems, this group was combined with group 8 (iron, ruthenium, osmium, and hassium) and group 10 (nickel, palladium, platinum, and darmstadtium) and called group "VIIIB" in the Chemical Abstracts Service (CAS) "U.S. system", or "VIII" in the old IUPAC (pre-1990) "European system" (and in Mendeleev's original table).

### Cobalt

Cobalt compounds have been used for centuries to impart a rich blue color to glass, glazes, and ceramics. Cobalt has been detected in Egyptian sculpture, Persian jewelry from the third millennium BC, in the ruins of Pompeii, destroyed in 79 AD, and in China, dating from the Tang dynasty (618–907 AD) and the Ming dynasty (1368–1644 AD).[5]

Swedish chemist Georg Brandt (1694–1768) is credited with discovering cobalt c. 1735, showing it to be a previously unknown element, distinct from bismuth and other traditional metals. Brandt called it a new "semi-metal".[6][7] He showed that compounds of cobalt metal were the source of the blue color in glass, which previously had been attributed to the bismuth found with cobalt. Cobalt became the first metal to be discovered since the pre-historical period. All other known metals (iron, copper, silver, gold, zinc, mercury, tin, lead and bismuth) had no recorded discoverers.

### Rhodium

William Hyde Wollaston

Rhodium was discovered in 1803 by William Hyde Wollaston,[8] soon after he discovered palladium.[9][10][11] He used crude platinum ore presumably obtained from South America.[12] His procedure dissolved the ore in aqua regia and neutralized the acid with sodium hydroxide (NaOH). He then precipitated the platinum as ammonium chloroplatinate by adding ammonium chloride (NH4Cl). Most other metals like copper, lead, palladium, and rhodium were precipitated with zinc. Diluted nitric acid dissolved all but palladium and rhodium. Of these, palladium dissolved in aqua regia but rhodium did not,[13] and the rhodium was precipitated by the addition of sodium chloride as Na3[RhCl6]·nH2O. After being washed with ethanol, the rose-red precipitate was reacted with zinc, which displaced the rhodium in the ionic compound and thereby released the rhodium as free metal.[14]

### Iridium

Chemists who studied platinum dissolved it in aqua regia (a mixture of hydrochloric and nitric acids) to create soluble salts. They always observed a small amount of a dark, insoluble residue.[15] In 1803, British scientist Smithson Tennant (1761–1815) analyzed the insoluble residue and concluded that it must contain a new metal. Vauquelin treated the powder alternately with alkali and acids[16] and obtained a volatile new oxide, which he believed to be of this new metal—which he named ptene, from the Greek word πτηνός ptēnós, "winged".[17][14] Tennant, who had the advantage of a much greater amount of residue, continued his research and identified the two previously undiscovered elements in the black residue, iridium and osmium.[15][16] He obtained dark red crystals (probably of Na2[IrCl6]·nH2O) by a sequence of reactions with sodium hydroxide and hydrochloric acid.[14] He named iridium after Iris (Ἶρις), the Greek winged goddess of the rainbow and the messenger of the Olympian gods, because many of the salts he obtained were strongly colored.[lower-alpha 1][18] Discovery of the new elements was documented in a letter to the Royal Society on June 21, 1804.[15][19]

### Meitnerium

Meitnerium was first synthesized on August 29, 1982, by a German research team led by Peter Armbruster and Gottfried Münzenberg at the Institute for Heavy Ion Research (Gesellschaft für Schwerionenforschung) in Darmstadt.[20] The team bombarded a target of bismuth-209 with accelerated nuclei of iron-58 and detected a single atom of the isotope meitnerium-266:[21]

20983Bi \+ 5826Fe → 266109Mt \+ n

This work was confirmed three years later at the Joint Institute for Nuclear Research at Dubna (then in the Soviet Union).[21]

## Properties

Z | Element | Electrons
per shell | M.P. | B.P. | Year of
Discovery | Discoverer

|
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|
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27 | cobalt | 2, 8, 15, 2 | 1768 K
1495 °C | 3200 K
2927 °C | ~1735 | Georg Brandt
45 | rhodium | 2, 8, 18, 16, 1 | 2237 K
1964 °C | 3968 K
3695 °C | 1803 | W. H. Wollaston
77 | iridium | 2, 8, 18, 32, 15, 2 | 2719 K
2446 °C | 4403 K
4130 °C | 1803 | S. Tennant
109 | meitnerium | 2, 8, 18, 32, 32, 15, 2[*] | — | — | 1982 | P. Armbruster and
G. Münzenberg

[*] Predicted.

The first three elements are hard silvery-white metals:

* Cobalt is a metallic element that can be used to turn glass a deep blue color. Cobalt is primarily used in lithium-ion batteries, and in the manufacture of magnetic, wear-resistant and high-strength alloys. The compounds cobalt silicate and cobalt(II) aluminate (CoAl2O4, cobalt blue) give a distinctive deep blue color to glass, ceramics, inks, paints and varnishes. Cobalt occurs naturally as only one stable isotope, cobalt-59. Cobalt-60 is a commercially important radioisotope, used as a radioactive tracer and for the production of high-energy gamma rays. Cobalt is also used in the petroleum industry as a catalyst when refining crude oil. This is to clean it of its sulfur content, which is very polluting when burned and causes acid rain.
* Rhodium can be used in jewelry as a shiny metal. Rhodium is a hard, silvery, durable metal that has a high reflectance. Rhodium metal does not normally form an oxide, even when heated. Oxygen is absorbed from the atmosphere only at the melting point of rhodium but is released on solidification. Rhodium has both a higher melting point and lower density than platinum. It is not attacked by most acids as it is completely insoluble in nitric acid and dissolves slightly in aqua regia.
* Iridium is mainly used as a hardening agent for platinum alloys. Iridium is the most corrosion-resistant metal known as it is not attacked by acids, including aqua regia. In the presence of oxygen, it reacts with cyanide salts. Traditional oxidants also react, including the halogens and oxygen at higher temperatures. Iridium also reacts directly with sulfur at atmospheric pressure to yield iridium disulfide.

All known isotopes of meitnerium are radioactive with short half-lives. Only minute quantities have been synthesized in laboratories. It has not been isolated in pure form, and its physical and chemical properties have not been determined yet. Based on what is known, meitnerium is considered a homologue to iridium.

## Biological role

Of the group 9 elements, only cobalt has a biological role. It is a key constituent of cobalamin, also known as vitamin B12, the primary biological reservoir of cobalt as an ultratrace element.[22][23] Bacteria in the stomachs of ruminant animals convert cobalt salts into vitamin B12, a compound which can only be produced by bacteria or archaea. A minimal presence of cobalt in soils therefore markedly improves the health of grazing animals, and an uptake of 0.20 mg/kg a day is recommended, because they have no other source of vitamin B12.[24]

Proteins based on cobalamin use corrin to hold the cobalt. Coenzyme B12 features a reactive C-Co bond that participates in the reactions.[25] In humans, B12 has two types of alkyl ligand: methyl and adenosyl. MeB12 promotes methyl (−CH3) group transfers. The adenosyl version of B12 catalyzes rearrangements in which a hydrogen atom is directly transferred between two adjacent atoms with concomitant exchange of the second substituent, X, which may be a carbon atom with substituents, an oxygen atom of an alcohol, or an amine. Methylmalonyl coenzyme A mutase (MUT) converts MMl-CoA to Su-CoA, an important step in the extraction of energy from proteins and fats.[26]

## See also

* Iron group
* Platinum group

## Notes

1. ↑ Iridium literally means "of rainbows".

## References

1. ↑ Fluck, E. (1988). "New Notations in the Periodic Table". Pure Appl. Chem. 60 (3): 431–436. doi:10.1351/pac198860030431. http://www.iupac.org/publications/pac/1988/pdf/6003x0431.pdf. Retrieved 24 March 2012.
2. ↑ 2.0 2.1 Leigh, G. J. Nomenclature of Inorganic Chemistry: Recommendations 1990. Blackwell Science, 1990. p. 283. ISBN 0-632-02494-1.
3. ↑ "Group 9: Transition Metals" (in en). 2020-08-15. https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/3_d-Block_Elements/Group_09:_Transition_Metals.
4. ↑ "Spot metal prices in USD" (in en). 2025-03-20. https://www.dailymetalprice.com/metalpricescurr.php?x=USD.
5. ↑ Cobalt, Encyclopædia Britannica Online.
6. ↑ Georg Brandt first showed cobalt to be a new metal in: G. Brandt (1735) "Dissertatio de semimetallis" (Dissertation on semi-metals), Acta Literaria et Scientiarum Sveciae (Journal of Swedish literature and sciences), vol. 4, pages 1–10.
See also: (1) G. Brandt (1746) "Rön och anmärkningar angäende en synnerlig färg—cobolt" (Observations and remarks concerning an extraordinary pigment—cobalt), Kongliga Svenska vetenskapsakademiens handlingar (Transactions of the Royal Swedish Academy of Science), vol. 7, pp. 119–130; (2) G. Brandt (1748) "Cobalti nova species examinata et descripta" (Cobalt, a new element examined and described), Acta Regiae Societatis Scientiarum Upsaliensis (Journal of the Royal Scientific Society of Uppsala), 1st series, vol. 3, pp. 33–41; (3) James L. Marshall and Virginia R. Marshall (Spring 2003) "Rediscovery of the Elements: Riddarhyttan, Sweden". The Hexagon (official journal of the Alpha Chi Sigma fraternity of chemists), vol. 94, no. 1, pages 3–8.
7. ↑ Wang, Shijie (2006). "Cobalt—Its recovery, recycling, and application". Journal of the Minerals, Metals and Materials Society 58 (10): 47–50. doi:10.1007/s11837-006-0201-y. Bibcode: 2006JOM....58j..47W.
8. ↑ Wollaston, W. H. (1804). "On a New Metal, Found in Crude Platina". Philosophical Transactions of the Royal Society of London 94: 419–430. doi:10.1098/rstl.1804.0019. https://books.google.com/books?id=7AZGAAAAMAAJ&pg=PA419.
9. ↑ Griffith, W. P. (2003). "Rhodium and Palladium – Events Surrounding Its Discovery". Platinum Metals Review 47 (4): 175–183. doi:10.1595/003214003X474175183. http://www.platinummetalsreview.com/dynamic/article/view/47-4-175-183.
10. ↑ Wollaston, W. H. (1805). "On the Discovery of Palladium; With Observations on Other Substances Found with Platina". Philosophical Transactions of the Royal Society of London 95: 316–330. doi:10.1098/rstl.1805.0024.
11. ↑ Usselman, Melvyn (1978). "The Wollaston/Chenevix controversy over the elemental nature of palladium: A curious episode in the history of chemistry". Annals of Science 35 (6): 551–579. doi:10.1080/00033797800200431.
12. ↑ Lide, David R. (2004). CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data. Boca Raton: CRC Press. pp. 4–26. ISBN 978-0-8493-0485-9. https://archive.org/details/crchandbookofche81lide/page/4.
13. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1113. ISBN 978-0-08-037941-8.
14. ↑ 14.0 14.1 14.2 Griffith, W. P. (2003). "Bicentenary of Four Platinum Group Metals: Osmium and iridium – events surrounding their discoveries". Platinum Metals Review 47 (4): 175–183. doi:10.1595/003214003X474175183.
15. ↑ 15.0 15.1 15.2 Hunt, L. B. (1987). "A History of Iridium". Platinum Metals Review 31 (1): 32–41. doi:10.1595/003214087X3113241. https://technology.matthey.com/documents/496120/626258/pmr-v31-i1-032-041.pdf/. Retrieved 2023-10-12.
16. ↑ 16.0 16.1 Emsley, J. (2003). "Iridium". Nature's Building Blocks: An A–Z Guide to the Elements. Oxford, England, UK: Oxford University Press. pp. 201–204. ISBN 978-0-19-850340-8. https://archive.org/details/naturesbuildingb0000emsl/page/201.
17. ↑ Thomson, T. (1831). A System of Chemistry of Inorganic Bodies. 1. Baldwin & Cradock, London; and William Blackwood, Edinburgh. p. 693. https://archive.org/details/asystemchemistr07thomgoog.
18. ↑ Weeks, M. E. (1968). Discovery of the Elements (7th ed.). Journal of Chemical Education. pp. 414–418. ISBN 978-0-8486-8579-9. OCLC 23991202. https://archive.org/details/discoveryofeleme0000week.
19. ↑ Tennant, S. (1804). "On Two Metals, Found in the Black Powder Remaining after the Solution of Platina". Philosophical Transactions of the Royal Society of London 94: 411–418. doi:10.1098/rstl.1804.0018. https://zenodo.org/record/1432312.
20. ↑ Münzenberg, G.; Armbruster, P.; Heßberger, F. P.; Hofmann, S.; Poppensieker, K.; Reisdorf, W.; Schneider, J. H. R.; Schneider, W. F. W. et al. (1982). "Observation of one correlated α-decay in the reaction 58Fe on 209Bi→267109". Zeitschrift für Physik A 309 (1): 89. doi:10.1007/BF01420157. Bibcode: 1982ZPhyA.309...89M.
21. ↑ 21.0 21.1 Barber, R. C.; Greenwood, N. N.; Hrynkiewicz, A. Z.; Jeannin, Y. P.; Lefort, M.; Sakai, M.; Ulehla, I.; Wapstra, A. P. et al. (1993). "Discovery of the transfermium elements. Part II: Introduction to discovery profiles. Part III: Discovery profiles of the transfermium elements". Pure and Applied Chemistry 65 (8): 1757. doi:10.1351/pac199365081757. (Note: for Part I see Pure Appl. Chem., Vol. 63, No. 6, pp. 879–886, 1991)
22. ↑ Yamada, Kazuhiro (2013). "Chapter 9. Cobalt: Its Role in Health and Disease". in Astrid Sigel. Interrelations between Essential Metal Ions and Human Diseases. Metal Ions in Life Sciences. 13. Springer. pp. 295–320. doi:10.1007/978-94-007-7500-8_9. ISBN 978-94-007-7499-5.
23. ↑ Cracan, Valentin; Banerjee, Ruma (2013). "Chapter 10 Cobalt and Corrinoid Transport and Biochemistry". in Banci, Lucia. Metallomics and the Cell. Metal Ions in Life Sciences. 12. Springer. pp. 333–374. doi:10.1007/978-94-007-5561-1_10. ISBN 978-94-007-5560-4. electronic-book ISBN 978-94-007-5561-1 ISSN 1559-0836 electronic-ISSN 1868-0402.
24. ↑ Schwarz, F. J.; Kirchgessner, M.; Stangl, G. I. (2000). "Cobalt requirement of beef cattle – feed intake and growth at different levels of cobalt supply". Journal of Animal Physiology and Animal Nutrition 83 (3): 121–131. doi:10.1046/j.1439-0396.2000.00258.x.
25. ↑ Voet, Judith G.; Voet, Donald (1995). Biochemistry. New York: J. Wiley & Sons. p. 675. ISBN 0-471-58651-X. OCLC 31819701. https://archive.org/details/biochemistry00voet_0/page/675.
26. ↑ Smith, David M.; Golding, Bernard T.; Radom, Leo (1999). "Understanding the Mechanism of B12-Dependent Methylmalonyl-CoA Mutase: Partial Proton Transfer in Action". Journal of the American Chemical Society 121 (40): 9388–9399. doi:10.1021/ja991649a.

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Periodic table

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1 | H |  | He
2 | Li | Be |  | B | C | N | O | F | Ne
3 | Na | Mg |  | Al | Si | P | S | Cl | Ar
4 | K | Ca |  | Sc | Ti | V | Cr | Mn | Fe | Co | Ni | Cu | Zn | Ga | Ge | As | Se | Br | Kr
5 | Rb | Sr |  | Y | Zr | Nb | Mo | Tc | Ru | Rh | Pd | Ag | Cd | In | Sn | Sb | Te | I | Xe
6 | Cs | Ba | La | Ce | Pr | Nd | Pm | Sm | Eu | Gd | Tb | Dy | Ho | Er | Tm | Yb | Lu | Hf | Ta | W | Re | Os | Ir | Pt | Au | Hg | Tl | Pb | Bi | Po | At | Rn
7 | Fr | Ra | Ac | Th | Pa | U | Np | Pu | Am | Cm | Bk | Cf | Es | Fm | Md | No | Lr | Rf | Db | Sg | Bh | Hs | Mt | Ds | Rg | Cn | Nh | Fl | Mc | Lv | Ts | Og

| Alkali metal | Alkaline earth metal | Lan­thanide | Actinide | Transition metal | Post-​transition metal | Metalloid | Reactive nonmetal | Noble gas

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Periodic table

Periodic table forms|

| Standard|

* 18-column
* 32-column

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Alternative|

* Alternatives
* Janet's left step table

Extended|

* Extension beyond the 7th period
* Aufbau
* Fricke
* Pyykkö

Sets of elements|

| By periodic table structure|

| Groups|

* 1 (Alkali metals)
* 2 (Alkaline earth metals)
* 3
* 4
* 5
* 6
* 7
* 8
* 9
* 10
* 11
* 12
* 13
* 14
* 15 (Pnictogens)
* 16 (Chalcogens)
* 17 (Halogens)
* 18 (Noble gases)

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Periods|

* 1
* 2
* 3
* 4
* 5
* 6
* 7
* 8+
* Aufbau
* Fricke
* Pyykkö

Blocks|

* s-block
* p-block
* d-block
* f-block
* g-block
* Aufbau principle

By metallicity|

| Metals|

* Alkali metals
* Alkaline earth metals
* Lanthanides
* Actinides
* Transition metals
* Post-transition metals

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Metalloids|

* Lists of metalloids by source
* Dividing line

Nonmetals|

* Reactive nonmetals
* Noble gases

Other sets|

* Platinum-group metals (PGM)
* Rare-earth elements
* Refractory metals
* Precious metals
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Elements|

| Lists|

* By: Abundance (in humans)
* Atomic properties
* Nuclear stability
* Production
* Symbol

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Properties|

* Crystal structure
* Electron configuration
* Electronegativity
* Goldschmidt classification
* Term symbol

Data pages|

* Abundance
* Atomic radius
* Boiling point
* Critical point
* Density
* Elasticity
* Electrical resistivity
* Electron affinity
* Electron configuration
* Electronegativity
* Hardness
* Heat capacity
* Heat of fusion
* Heat of vaporization
* Ionization energy
* Melting point
* Oxidation state
* Speed of sound
* Thermal conductivity
* Thermal expansion coefficient
* Vapor pressure

History|

* Element discoveries
* Mendeleev's predictions
* Naming
* etymology
* controversies
* for places
* for people
* in East Asia

See also|

* IUPAC
* nomenclature
* systematic element name
* Trivial name
* Dmitri Mendeleev

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