Symbol	Os
Atomic number	76
Atomic mass	190.2 g.mol -1
Electronegativity according to Pauling	2.2
Density	22.5 g.cm-3 at 20°C
Melting point	3045 °C
Boiling point	5027 °C
Vanderwaals radius	0.136 nm
Ionic radius	0.067 nm (+4)
Isotopes	13
Electronic shell	[ Xe ] 4f14 5d- 6s2
Energy of first ionisation	838 kJ.mol -1
Standard potential	+ 0.85 V (Os2+/ Os )

Osmium

Osmium is lustrous, silvery metal, one of the so-called platinum group of metals. It is the densest metal known, althoung only by the narrowest margins. Osmium is uneffected by water and acids, but dissolves with molten alkalis. Osmium powder reacts slowly with the oxygen of the air and gives off detacteble amounts of osmium tetroxide vapour.

Applications

The metal is used in a few alloys and in industry as a catalyst. At one time it was to be encountered in the nibs of high-quality fountain pens, compass needles, long-life gramophone needles and clock bearings, thanks to its extreme hardness and corrosion resistance.

Osmium in the environment

Osmium is mainly found alloyed with other platinum metals, from which it is recovered commercially. The most important ores are either iridosmine and osmiridium. Iridosmine is a rare mineral found in Russia and in North and South America. Less of 100 Kg are produced each year. There is little demand for the metal, which is difficult to fabricate.

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