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Iridium Facts

Updated: Jan 14, 2022

Chemical & Physical Properties of Iridium

Iridium has a melting point of 2410°C, a boiling point of 4130°C, a specific gravity of 22.42 (17°C), and valence of 3 or 4. A member of the platinum family, iridium is white like platinum, but with a slight yellowish cast. The metal is very hard and brittle and is the most corrosion-resistant metal known. Iridium is not attacked by acids or aqua regia, but it is attacked by molten salts, including NaCl and NaCN. Either iridium or osmium is the densest known element, but the data do not allow for selection between the two.


The metal is used for hardening platinum. It is used in crucibles and other applications requiring high temperatures. Iridium is combined with osmium to form an alloy used in compass bearings and for tipping pens. Iridium is also used for electrical contacts and in the jewelry industry.

Sources of Iridium

Iridium occurs in nature uncombined or with platinum and other related metals in alluvial deposits. It is recovered as a by-product of the nickel mining industry.

Iridium Basic Facts

Atomic Number: 77

Symbol: Ir

Atomic Weight: 192.22

Discovery: S.Tenant, A.F.Fourcory, L.N.Vauquelin, H.V.Collet-Descoltils 1803/1804 (England/France)

Electron Configuration: [Xe] 6s2 4f14 5d7

Word Origin: Latin iris rainbow, because the salts of iridium are highly colored

Element Classification: Transition Metal

Iridium Physical Data

Density (g/cc): 22.42

Melting Point (K): 2683

Boiling Point (K): 4403

Appearance: white, brittle metal

Atomic Radius (pm): 136

Atomic Volume (cc/mol): 8.54

Covalent Radius (pm): 127

Ionic Radius: 68 (+4e)

Specific Heat (@20°C J/g mol): 0.133

Fusion Heat (kJ/mol): 27.61

Evaporation Heat (kJ/mol): 604

Debye Temperature (K): 430.00

Pauling Negativity Number: 2.20

First Ionizing Energy (kJ/mol): 868.1

Oxidation States: 6, 4, 3, 2, 1, 0, -1

Lattice Structure: Face-Centered Cubic

Lattice Constant (Å): 3.840

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