Discovery date : 1803
Discovered by: Smithson Tennant
Origin of the name: The name is derived from the Greek goddess of the rainbow, Iris.
Allotropes :
~>IRIDIUM 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 the second densest element (after osmium). It is also the most corrosion-resistant metal, even at temperatures as high as 2000C.
| FACT BOX | |||
| Group | 9 | Melting point | 2446°C, 4435°F, 2719 K |
| Period | 6 | Boiling point | 4428°C, 8002°F, 4701 K |
| Block | d | Density (g cm−3) | 22.5622 |
| Atomic number | 77 | Relative atomic mass | 192.217 |
| State at 20°C | Solid | Key isotopes | 193Ir |
| Electron configuration | [Xe] 4f145d76s2 | CAS number | 7439-88-5 |
| ChemSpider ID | 22367 | ChemSpider is a free chemical structure database | |
Iridium was discovered together with osmium in1803 by Smithson Tennant in London. When crude platinum was dissolved in dilute aqua regia, which is a mixture of nitric and hydrochloric acids, it left behind a black residue thought to be graphite. Tennant thought otherwise, and by treating it alternately with alkalis and acids he was able to separate it into two new elements. These he announced at the Royal Institution in London, naming one iridium, because its salts were so colourful and the other osmium because it had a curious odour (see osmium).
Despite its seeming intractability, a group of chemists, including the great Humphry Davy, demonstrated in 1813 that iridium would indeed melt like other metals. To achieve this they exposed it to the powerful current generated by a large array of batteries.