Iridium (Ir)

Very hard and brittle, silvery metallic transition element. It has a yellowish cast to it. Salts of iridium are highly colored. It is the most corrosion resistant metal known, not attacked by any acid, but is attacked by molten salts. There are two natural isotopes of iridium, and 4 radioisotopes, the most stable being Ir-192 with a half-life of 73.83 days. Ir-192 decays into Platinum, while the other radioisotopes decay into Osmium. Iridium is used in high temperature apparatus, electrical contacts, and as a hardening agent for platinumpy. Discovered in 1803 by Smithson Tennant in England. The name comes from the Greek word iris, which means rainbow. Iridium metal is generally non-toxic due to its relative unreactivity, but iridium compounds should be considered highly toxic.
Atomic Number77
Atomic Weight192.217
Mass Number193
Protons77 p+
Neutrons116 n0
Electrons77 e-
Iridium foil.jpg Animated Bohr Model Enhanced Bohr Model Bohr Model Orbital Diagram


Atomic Radius
135 pm
Atomic Volume
Covalent Radius
122 pm
Metallic Radius
127 pm
Ionic Radius
68 pm
Crystal Radius
82 pm
Van der Waals radius
213 pm
22.5622 g/cm³
Boiling Point
4,403 K
Melting Point
2,683 K
Electrons per shell2, 8, 18, 32, 15, 2
1.8724651211297 eV/particle
Proton Affinity
Electron Affinity
Ionization Potential
8.96702 eV/particle
Heat of Vaporization
604 kJ/mol
Heat of Fusion
27.61 kJ/mol
Heat of Formation
669 kJ/mol
Molar Heat Capacity
Specific Heat Capacity
0.131 J/(g⋅K)
Thermal Conductivity
Gas Basicity
Dipole Polarizability
54 a₀
C6 Dispersion Coefficient
Oxidation States-3, -1, 1, 2, 3, 4, 5, 6, 7, 8
Crystal StructureFace Centered Cubic (FCC)
Lattice Constant
3.84 Å
Bulk Modulus
Electrical Resistivity
Electron Configuration[Xe] 4f14 5d7 6s2
Magnetic Ordering
Magnetic Susceptibility
Poisson Ratio
Shear Modulus
Young's Modulus
Alternate Names
Adiabatic Index
Electric Conductivity
Critical Pressure
Critical Temperature
Curie Point
Magnetic Susceptibility
Neel Point
Neutron Cross Section
Neutron Mass Absorption
Gas Phase
Quantum Numbers
Refractive Index
Space Group
Speed of Sound
Superconducting Point
Thermal Expansion
Valence Electrons
CategoryTransition metals, Transition metals
Glawe Number62
Mendeleev Number65
Pettifor Number65
Geochemical Classnoble metal
Goldschmidt Classsiderophile
Decay Mode
Abundance in Earth's crust
0.001 mg/kg
Abundance in Oceans
Abundance in Human Body
Abundance in Meteor
Abundance in Sun
Abundance in Universe2×10-7%

Isotopes of Iridium

Stable Isotopes
191Ir 193Ir
Unstable Isotopes
164Ir 165Ir 166Ir 167Ir 168Ir 169Ir 170Ir 171Ir 172Ir 173Ir 174Ir 175Ir 176Ir 177Ir 178Ir 179Ir 180Ir 181Ir 182Ir 183Ir 184Ir 185Ir 186Ir 187Ir 188Ir 189Ir 190Ir 192Ir 194Ir 195Ir 196Ir 197Ir 198Ir 199Ir


Iridium was discovered in 1803 by English chemist Smithson Tennant in London. Chemists who studied platinum dissolved it in aqua regia to create soluble salts and observed a small amount of a dark, insoluble residue. Smithson Tennant analyzed the insoluble residue and concluded that it must contain a new metal. From the Latin word iris meaning rainbow

DiscoverersS.Tenant, A.F.Fourcory, L.N.Vauquelin, H.V.Collet-Descoltils
Discovery LocationEngland/France
Discovery Year1804
Name OriginLatin: iris (rainbow).
Iridium is considered to be of low toxicity
Iridium is the most corrosion-resistant metal known


Iridium is used in making crucibles and other equipment that is used at high temperatures. Iridium is also used as a hardening agent in platinum alloys. Its resistance to arc erosion makes iridium alloys ideal for electrical contacts for spark plugs. Radioactive isotopes of iridium are used in radiation therapy for the treatment of cancer. Used with osmium to tip gold pen points, to make crucible and special containers. Also to make alloys used for standard weights and measures, and heat-resistant alloys. Also as hardening agent for platinum.


Found in gravel deposits with platinum.