Chemistry:Group 9 element

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Short description: Group of chemical elements

Group 9, by modern IUPAC numbering,[1] is a group (column) of chemical elements in the periodic table. Members of Group 9 include cobalt (Co), rhodium (Rh), iridium (Ir) and meitnerium (Mt).[2] These are all transition metals in the d-block, considered to be some of the most rare of which.[3]

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.

"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).


Z Element No. of electrons
per shell
M.P. B.P. Year of
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.

Rhodium can be used in jewelry as a shiny metal.

Iridium is mainly used as a hardening agent for platinum alloys.

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.

See also