Symbol	Ir
Atomic number	77
Group	9 (Cobalt group)
Period	6
Block	d
Classification	Transition Metal

Appearance	Silvery white
Color	Silver

Number of protons	77 p+
Number of neutrons	115 n0
Number of electrons	77 e-

From Wikipedia, the free encyclopediaIridium is a chemical element with symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, iridium is generally credited with being the second densest element (after osmium) based on measured density, although calculations involving the space lattices of the elements show that iridium is denser. It is also the most corrosion-resistant metal, even at temperatures as high as 2000 °C. Although only certain molten salts and halogens are corrosive to solid iridium, finely divided iridium dust is much more reactive and can be flammable.

Phase at STP	Solid
Density	22.56 g/cm3
Atomic weight	192.217 u

Melting point	2719 K 2445.85 °C 4434.53 °F
Boiling point	4403 K 4129.85 °C 7465.73 °F
Heat of vaporization	563.58 kJ/mol

Electronegativity (Pauling Scale)	2.2
Electron affinity	150.94 kJ/mol
Oxidation states	−3, −1, 0, +1, +2, +3, +4, +5, +6, +7, +8, +9 ()
Ionization energies	880 kJ/mol 1600 kJ/mol

Electron configuration Shorthand configuration	[Xe] 4f14 5d7 6s2
Electron configuration Full configuration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d7 6s2
Electron configuration chart	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d7 6s2
Electrons per shell	2, 8, 18, 32, 15, 2
Valence electrons	2
Valency electrons	2,3,4
Bohr model	Figure: Shell diagram of Iridium (Ir) atom.
Orbital Diagram 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 6s

Discovery and first isolation

Smithson Tennant (1803)

Discovery of 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. Joseph Louis Proust thought that the residue was graphite. The French chemists Victor Collet-Descotils, Antoine François, comte de Fourcroy, and Louis Nicolas Vauquelin also observed the black residue in 1803, but did not obtain enough for further experiments. In 1803, British scientist Smithson Tennant analyzed the insoluble residue and concluded that it must contain a new metal. Vauquelin treated the powder alternately with alkali and acids 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". 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. He obtained dark red crystals by a sequence of reactions with sodium hydroxide and hydrochloric acid. 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. Discovery of the new elements was documented in a letter to the Royal Society on June 21, 1804.

CAS Number	7439-88-5
ChemSpider ID	22367
EC number	231-095-9
PubChem CID Number	23924