Chemical Elements History and Information Iridium

About the chemical element Iridium, its symbol, atomic number and weight, who discovered it and when.

The Atomic Elements and Their Uses

(Element) (Symbol) (Atomic number) (Atomic weight)

Iridium Ir 77 192.22

Discovered by Smithson Tennant of England in 1804. The world standards of mass and length--kept in a Paris vault--are made from an iridium and platinum alloy. This alloy is used for the standards because it is chemically inert, has a very high melting point, and expands or contracts very little with temperature changes.