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Iridium (Ir)

Iridium is a chemical element of the periodic table with chemical symbol Ir and atomic number 77 with an atomic weight of 192.217 u and is classed as transition metal and is part of group 9 (cobalt group). Iridium is solid at room temperature.

Iridium in the periodic table

Atomic number77
Group9 (Cobalt group)
ClassificationTransition Metal
AppearanceSilvery white
Color Silver
Number of protons77 p+
Number of neutrons115 n0
Number of electrons77 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.

Physical properties

Phase at STPSolid
Density22.56 g/cm3
Atomic weight192.217 u

Thermal properties

Melting point2719 K
2445.85 °C
4434.53 °F
Boiling point4403 K
4129.85 °C
7465.73 °F
Heat of vaporization563.58 kJ/mol

Atomic properties

Electronegativity (Pauling Scale)2.2
Electron affinity150.94 kJ/mol
Oxidation states−3, −1, 0, +1, +2, +3, +4, +5, +6, +7, +8, +9
Ionization energies
  1. 880 kJ/mol
  2. 1600 kJ/mol

Electron configuration for iridium

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
Electrons per shell2, 8, 18, 32, 15, 2
Valence electrons 2
Valency electrons 2,3,4
Bohr model
IridiumElectron shell for Iridium, created by Injosoft ABIr
Figure: Shell diagram of Iridium (Ir) atom.
Orbital Diagram

The history of Iridium

Discovery and first isolationSmithson 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.


List of unique identifiers for Iridium in various chemical registry databases
CAS Number7439-88-5
ChemSpider ID22367
EC number231-095-9
PubChem CID Number23924