Osmium is in Row 6 of the periodic table, one of the elements known as the transition metals. It has an atomic number of 76, an atomic mass of 190.2, and a chemical symbol of Os.

Properties

Osmium is a bluish white, shiny metal with a melting point of about 5,400°F (about 3,000°C), and a density of 22.5 grams per cubic centimeter. These values are all among the highest for the elements. Osmium is not very ductile, malleable, or, in general, workable, thereby reducing the number of practical applications it has. It is a relatively inactive element, combining with oxygen only at high temperatures and reacting only with acids after long exposure.

Occurrence and Extraction

Osmium is very rare with an abundance no greater than about one part per billion in the Earth's crust. Its most common ore is osmiridium. The element occurs in all ores of platinum. It is obtained commercially as a byproduct of the extraction of platinum from its ores.

Discovery and Naming

Osmium was discovered in 1804 by the English chemist Smithson Tennant. Tennant was analyzing the element platinum and found that he continually obtained an unusual black powder with properties different from that of platinum itself. Tennant was eventually able to determine that the black powder was a mixture of two new elements, osmium and iridium. He suggested the name osmium for one of the elements from the Greek word osme, meaning "odor." The name came from one of the osmium compounds with which Tennant was working, osmium tetroxide (OsO₄).

Uses

Osmium has relatively few uses, its primary application being in alloys with platinum or iridium. The addition of small amounts of osmium to these metals greatly increases their hardness. Osmium alloys are sometimes used in pen tips and in specialized laboratory equipment.

Health Issues

Osmium tetroxide is a particularly interesting compound. It has considerable demand for use as a catalyst in research, but it is highly reactive and very toxic. It is shipped in small glass containers that carry no labels and are not marked in ink. The compound would react violently with either label or ink, so instructions provided separately explain how to use the material.