Iridium (Ir)
Stable isotopes of iridium available from ISOFLEX
| Isotope | Z(p) | N(n) | Atomic Mass | Natural Abundance | Enrichment Level | Chemical Form |
| Ir-191 | 77 | 114 | 190.960591 | 37.30% | >93.00% | Metal |
| Ir-193 | 77 | 116 | 192.962923 | 62.70% | 98.40% | Metal |
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Other isotopes of iridium available from ISOFLEX
| Isotope | Z(p) | N(n) | Atomic Mass | Half-life | Specific Activity | Form |
| Ir-192 | 77 | 115 | 191.962602 | 73.83 days | ~550-600 curies/g at calibration | Iridium metal discs |
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Iridium was discovered in 1803 by French chemists Victor Collet-Descotils, Antoine François Comte de Fourcroy and Louis Nicolas Vauquelin, and British scientist Smithson Tennant. It is named for Iris, the Greek winged goddess of the rainbow and messenger of the Olympic gods.
A silver-white metal with low ductility and close-packed cubic crystals, iridium does not tarnish in air. On heating strongly, a slightly volatile oxide is formed. It is insoluble in acid and slowly soluble in aqua regia and in fused alkalis. It is the most corrosion-resistant element and is highly resistant to chemical attack at ordinary temperatures. At elevated temperatures (near 600 ºC), iridium metal combines with oxygen to form a coating of iridium dioxide. Similarly, the metal reacts with halogens only at elevated temperatures. Iridium forms alloys with several metals, mostly platinum group metals. Iridium does not react with concentrated acids or with molten alkalis.
The most important use of iridium is as an alloying metal for platinum and palladium. Iridium enhances the resistance of platinum to chemical attack and corrosion, as well as its enhancing hardness and tensile strength. Such alloys are used for jewelry, decorative purposes, electrical contacts, thermocouples, crucibles, electrodes, hypodermic needles and medical accessories. The radioisotope Iridium-192 is used in the examination of ferrous welds and in other radiographic applications.
Properties of Iridium
| Name | Iridium |
| Symbol | Ir |
| Atomic number | 77 |
| Atomic weight | 192.22 |
| Standard state | Solid at 298 ºK |
| CAS Registry ID | 7439-88-5 |
| Group in periodic table | 9 |
| Group name | Precious metal or platinum group metal |
| Period in periodic table | 6 |
| Block in periodic table | d-block |
| Color | Silvery white |
| Classification | Metallic |
| Melting point | 2410 °C |
| Boiling point | 4130 °C |
| Vaporization point | 4130 °C |
| Thermal conductivity | 147 W/(m·K) at 298.2 °K |
| Electrical resistivity | 5.3 µΩ·cm at 20 °C |
| Electronegativity | 2.2 |
| Specific heat | 0.133 kJ·mol-1 at 20 °C |
| Heat of vaporization | 560 kJ·mol-1 at 4130 °C |
| Heat of fusion | 26 kJ·mol-1 |
| Density of liquid | 19 g/cm3 at 2410 °C |
| Density of solid | 22.42 g/cm3 (highest among metals) |
| Mohs hardness scale | 6.0-6.5 |
| Electron configuration | [Xe]4f145d76s2 |
| Oxidation states | 0, +1, +2, +3, +4, +5, +6 |
| Common oxidation states | +3, +4 |
