IRIDIUM
TRANSITION ELEMENT: COBALT GROUP
| Atomic number: | 77 |
| Group numbers: | 9 |
| Period: | 6 |
| Electronic configuration: | [Xe] 4f14 5d7 6s2 |
| Formal oxidation number: | +3 +4 |
| Electronegativities: | 2.2 |
| Atomic radius / pm: | 135.7 |
| Relative atomic mass: | 192.217(3) |
Iridium was discovered by Smithson Tennant (GB) in 1803. The origin of the name comes from the Latin word iris, meaning rainbow, because its salts are highly coloured. It is a heavy, brittle, white metal that is unreactive in air, water and acids but reacts with fused NaOH. Metal ignites and burns readily. Iridium is found in gravel deposits with platinum. It is 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. It is used as a hardening agent for platinum. The price of 99.95 % pure iridium sponge is 829.60 € for 10 g.
| Density / g dm-3: | 22420 | (290 K) |
| 20000 | (m.p.) | |
| Molar volume / cm3mol-1: | 8.57 | (290 K) |
| 8.74 | (m.p.) | |
| Electrical resistivity / µΩcm: | 5.3 | (20 °C) |
| Thermal conductivity / W m-1K-1: | 147 |
| Melting point / °C: | 2446 |
| Boiling point / °C: | 4428 |
| Heat of fusion / kJ mol-1: | 26.4 |
| Heat of vaporization / kJ mol-1: | 612.1 |
| Heat of atomization / kJ mol-1: | 664.34 |
| First ionization energy / kJ mol-1: | 865.19 |
| Second ionization energy / kJ mol-1: | - |
| Third ionization energy / kJ mol-1: | - |
| in the atmosphere / ppm: | - |
| in the Earth's crust / ppm: | 0.0001 |
| in the oceans / ppm: | - |
| Crystal structure: | face-centered cubic |
| Unit-cell dimensions / pm: | a=383.92 |
| Space group: | Fm3m |
| Isotope | Relative atomic mass | Mass percent (%) |
|---|---|---|
| 191Ir | 190.960591(3) | 37.3(5) |
| 193Ir | 192.962924(3) | 62.7(5) |
| Balanced half-reaction | Eo / V | |
|---|---|---|
| Ir3+ + 3e- → Ir(s) | +1.15 | |
| IrCl62- + e- → IrCl63- | +1.026 | |
| IrCl62- + 4e- → Ir(s) + 6Cl- | +0.835 | |
| IrCl63- + 3e- → Ir(s) + 6Cl- | +0.77 | |
| IrO2(s) + 4H+ + 4e- → Ir(s) + H2O | +0.93 | |
| IrO2(s) + 2H2O + 4e- → Ir(s) + 4OH- | +0.1 | |
| Ir2O3 + 3H2O + 6e- → 2Ir(s) + 6OH- | +0.1 |
| 76 Osmium | ← | 77 Iridium | → | 78 Platinum |
Citing this page:
Generalic, Eni. "Iridium." EniG. Periodic Table of the Elements. KTF-Split, 18 Jan. 2024. Web. {Date of access}. <https://www.periodni.com/ir.html>.
