Osmium << OZ mee uhm >> is a hard metallic element. It is one of the densest elements, with a density of 22.57 grams per cubic centimeter. Osmium is rare and expensive and is found in the same ores as platinum.
Osmium occurs in several large deposits spread around the world and in meteorites. Refined osmium is a fine, black powder or a hard, blue-gray mass. Osmium alloys, which resist corrosion, are used to tip penpoints and in mechanical parts. When heated in air, osmium forms osmium tetroxide, which vaporizes at about 100 °C. This compound can damage the eyes, skin, and lungs. It is used in certain scientific processes.
Osmium’s chemical symbol is Os. The element has a boiling point of 5012 plus or minus 100 °C and a melting point of 3033 plus or minus 30 °C. Its atomic number (number of protons in its nucleus) is 76. Its relative atomic mass is 190.23. An element’s relative atomic mass equals its mass (amount of matter) divided by 1/12 of the mass of carbon 12, the most abundant form of carbon.
Chemists classify osmium as a transition metal . For information on the position of osmium on the periodic table, see the article Periodic table .
Smithson Tennant, a British chemist, discovered osmium in 1804.
