Group 9 element

Group 9 in the periodic table
Name by element	cobalt group
CAS group number; (US, pattern A-B-A)	part of VIIIB
old IUPAC number; (Europe, pattern A-B)	part of VIII

↓ 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

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.

^ Fluck, E. (1988). "New Notations in the Periodic Table" (PDF). Pure Appl. Chem. 60 (3): 431–436. doi:10.1351/pac198860030431. S2CID 96704008. Retrieved 24 March 2012.
^ Leigh, G. J. Nomenclature of Inorganic Chemistry: Recommendations 1990. Blackwell Science, 1990. p. 283. ISBN 0-632-02494-1.
^ "Group 9: Transition Metals". Chemistry LibreTexts. 2020-08-15. Retrieved 2022-03-24.
^ "Spot metal prices in USD". Daily Metal Prices. 2025-03-20. Retrieved 2025-03-20.

[1] Fluck, E. (1988). "New Notations in the Periodic Table" (PDF). Pure Appl. Chem. 60 (3): 431–436. doi:10.1351/pac198860030431. S2CID 96704008. Retrieved 24 March 2012.

[leigh-2] Leigh, G. J. Nomenclature of Inorganic Chemistry: Recommendations 1990. Blackwell Science, 1990. p. 283. ISBN 0-632-02494-1.

[3] "Group 9: Transition Metals". Chemistry LibreTexts. 2020-08-15. Retrieved 2022-03-24.

[4] "Spot metal prices in USD". Daily Metal Prices. 2025-03-20. Retrieved 2025-03-20.

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