All practice pages/Interatomic theory/Elements
Element 77, a transition metal
The most corrosion-resistant metal, and the element whose thin layer in rock revealed the asteroid that ended the dinosaurs.
Period 6, group 9. The other transition metals are tinted, and every cell opens its own article.
Like other transition metals, iridium loses its outer s electrons, and often some d electrons as well, to form positive ions, and it can form more than one kind.
One of the rarest elements in the crust, found with platinum in South Africa and Russia. Meteorites carry much more, which is why a thin iridium-rich clay layer, found by Luis and Walter Alvarez in 1980, marks a giant asteroid impact 66 million years ago.
Smithson Tennant found it in 1803, together with osmium, in the residue of platinum ore. He named it after Iris, the Greek goddess of the rainbow, for the many colors of its salts.
Spark plug tips, crucibles for growing crystals at very high temperatures, and electrodes for making chlorine and hydrogen. Iridium compounds give off the light in many OLED screens, iridium-192 is used in cancer radiotherapy and to X-ray welds, and the old international prototype kilogram was an alloy of platinum and iridium.