Osmium - Os General Information Discovery Osmium was discovered by S. Tennant in 1803 in London. Appearance Osmium is lustrous, bluish-white, extremely hard and has a pungent smell. Source Osmium occurs in the free state and in the mineral osmiridium, but commercial recovery is from the wastes of nickel refining. Uses Osmium is almost entirely used to produce very hard alloys for fountain pen tips, instrument pivots, needles and electrical contacts. Biological Role Osmium has no known biological role, but is very toxic, and can cause lung, skin and eye damage. General Information Osmium metal is unaffected by air, water and acids, but reacts with molten alkalis. The powdered metal slowly gives off osmium(VIII) oxide, the source of its pungent odour.

	Physical Information
	Atomic Number		76
	Relative Atomic Mass (12C=12.000)		190.2
	Melting Point/K		3327
	Boiling Point/K		5300
	Density/kg m-3		22590 (293K)
	Ground State Electron Configuration		[Xe]4f145d66s2
	Electron Affinity(M-M-)/kJ mol-1		-139

	Key Isotopes
	nuclide	184Os	185Os	186Os	187Os	188Os
	atomic mass	184.0		186.0	187.0	188.0
	natural abundance	0.02%	0%	1.58%	1.6%	13.3%
	half-life	stable	97 days	stable	stable	stable
	nuclide	189Os	190Os	191Os	192Os
	atomic mass	189.0	190.0		191.9
	natural abundance	16.1%	26.4%	0%	41%
	half-life	stable	stable	15 days	stable

Other Information
Enthalpy of Fusion/kJ mol-1		29.3
Enthalpy of Vaporisation/kJ mol-1		738
Oxidation States
main	Os+4
others	Os-2, Os0, Os+1, Os+2, Os+3,
	Os+5, Os+6, Os+7, Os+8

	Ionisation Energies/kJ mol-1
	M - M+	840
	M+ - M2+	1600
	M2+ - M3+	2400
	M3+ - M4+	3900
	M4+ - M5+	5200
	M5+ - M6+	6600
	M6+ - M7+	8100
	M7+ - M8+	9500
	M8+ - M9+
	M9+ - M10+