Group 9 element

Group →	4
↓ Period
4	27 Co
5	45 Rh
6	77 Ir
7	109 Mt
Legend Transition metal Primordial element Synthetic

In modern IUPAC nomenclature, Group 9 of the periodic table contains the elements cobalt (Co), rhodium (Rh), iridium (Ir), and meitnerium (Mt). These are all d-block transition metals. All known isotopes of Mt are radioactive with short half-lives, and it is not known to occur in nature; only minute quantities have been synthesized in laboratories.

Like other groups, the members of this family show patterns in its electron configuration, especially the outermost shells resulting in trends in chemical behavior, though rhodium curiously does not follow the pattern:

Chemistry

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

Group 9 in the periodic table

Z	Element	No. of electrons/shell
27	cobalt	2, 8, 15, 2
45	rhodium	2, 8, 18, 16, 1
77	iridium	2, 8, 18, 32, 15, 2
109	meitnerium	2, 8, 18, 32, 32, 15, 2

Meitnerium has not been isolated in pure form, and its properties have not been conclusively observed; only cobalt, rhodium, and iridium have had their properties experimentally confirmed. All three elements are typical silvery-white transition metals, hard, and have high melting and boiling points.

History

Cobalt has been discovered in Egyptian and Persian artifacts from before the 2nd millennium BCE. Rhodium was discovered in 1803 when William Hyde Wollaston dissolved platinum ore in aqua regia, then neutralized the acid with sodium hydroxide. Wollaston then added ammonium chloride, and dissolved all metals except rhodium and palladium with the nitric acid in the aqua regia. Iridium was discovered in a very similar way in 1804 by Smithson Tennant. Meitnerium was discovered in 1982 by bombarding bismuth-209 with iron-58.

Occurrence

All group 9 elements are relatively rare in the earth's crust, with the most abundant, cobalt, only accounting for 0.0029% of the Earth's crust. Rhodium and Iridium are two of the rarest naturally occurring elements in the earth, only found in platinum ores. Meitnerium has only been produced in nuclear reactors and has never been observed in nature nor isolated in pure form.

Biological occurrence

Cobalt is an essential trace nutrient to all animals, found in vitamin B-12. Rhodium, Iridium, and Meitnerium have no known biological roles.

Applications

• Alloys with other metals, primarily to add corrosion and wear resistance
• Industrial Catalysts
• Superalloys
• Electrical Components

See also

• Platinum group

Explanation of right side periodic table slice:

Transition metals

atomic number in black are solids

solid borders are older than the Earth (Primordial elements)

dashed borders have no isotopes older than the earth