Chromium - Cr General Information Discovery Chromium was discovered in 1780 by N.E. Vanquelin in Paris. Appearance Chromium is a blue-white, hard metal, capable of taking a high polish. Source Chromium is found principally in the ore chromite, which is found in many places including the former USSR, Turkey, Iran, Finland and the Philippines. Chromium metal is usually produced commercially by reduction of chromium(III) oxide by aluminium, or by electrolysis of chrome alum. Uses Chromium is used to harden steel, to manufacture stainless steel and to produce several alloys. It is also used in plating as it prevents corrosion and gives a high-lustre finish. It is also used as a catalyst. Chromium compounds are valued as pigments for their vivid green, yellow, red and orange colours. The ruby takes its colour from chromium, and chromium added to glass imparts an emerald green colour. Biological Role Chromium is an essential trace element, but is carcinogenic in excess. Chromium compounds are toxic.

	Physical Information
	Atomic Number		24
	Relative Atomic Mass (12C=12.000)		51.996
	Melting Point/K		2130
	Boiling Point/K		2945
	Density/kg m-3		7190 (293K)
	Ground State Electron Configuration		[Ar]3d54s1
	Electron Affinity(M-M-)/kJ mol-1		-94

	Key Isotopes
	nuclide	50Cr	51Cr	52Cr	53Cr	54Cr
	atomic mass	49.946	50.945	51.941	52.941	53.939
	natural abundance	4.359%	0%	83.79%	9.5%	2.36%
	half-life	stable	27.8 days	stable	stable	stable

Other Information
Enthalpy of Fusion/kJ mol-1		15.3
Enthalpy of Vaporisation/kJ mol-1		341.8
Oxidation States
main	Cr+3
others	Cr-2, Cr-1, Cr0, Cr+1, Cr+2
	Cr+4, Cr+5, Cr+6

	Ionisation Energies/kJ mol-1
	M - M+	652.7
	M+ - M2+	1592
	M2+ - M3+	2987
	M3+ - M4+	4740
	M4+ - M5+	6690
	M5+ - M6+	8738
	M6+ - M7+	15550
	M7+ - M8+	17830
	M8+ - M9+	20220
	M9+ - M10+	23580