Barium - Ba General Information Discovery Barium was discovered by Sir Humphry Davy in 1808 in London. Appearance Barium is a relatively soft, silvery-white metal resembling lead. It oxidises very easily and is therefore stored under petroleum or in an inert gas atmosphere. Source Barium occurs only in combination with other elements, chiefly in the ores barytes and witherite. It can be prepared by electrolysis of the chloride, or by heating barium oxide with aluminium. Uses Barium is not an extensively used element. The best-known use is in the form of barium sulfate, which can be drunk as a medical cocktail to outline the stomach and intestines for medical examination. The sulfate is also used in paint and in glassmaking. Barium carbonate has been used as a rat poison. Barium nitrate gives fireworks a green colour. Biological Role Barium and all its compounds that are water or acid soluble are toxic. General Information Barium combines with air, and reacts rapidly with water and alcohol.

	Physical Information
	Atomic Number		56
	Relative Atomic Mass (12C=12.000)		137.33
	Melting Point/K		1002
	Boiling Point/K		1910
	Density/kg m-3		3594 (293K)
	Ground State Electron Configuration		[Xe]6s2
	Electron Affinity(M-M-)/kJ mol-1		+46

	Key Isotopes
	nuclide	130Ba	132Ba	133Ba	134Ba	135Ba
	atomic mass	129.9	131.9		133.9	134.9
	natural abundance	0.106%	0.101%	0%	2.417%	6.592%
	half-life	stable	stable	10.53 yrs	stable	stable
	nuclide	136Ba	137Ba	138Ba	140Ba
	atomic mass	135.9	136.9	137.9
	natural abundance	7.854%	11.32%	71.7%	0%
	half-life	stable	stable	stable	12.7 days

Other Information
Enthalpy of Fusion/kJ mol-1		7.66
Enthalpy of Vaporisation/kJ mol-1		150.9
Oxidation States
Ba+2

	Ionisation Energies/kJ mol-1
	M - M+	502.8
	M+ - M2+	965.1
	M2+ - M3+	3600
	M3+ - M4+	4700
	M4+ - M5+	6000
	M5+ - M6+	7700
	M6+ - M7+	9000
	M7+ - M8+	10200
	M8+ - M9+	13500
	M9+ - M10+	15100