Actinium - Ac General Information Discovery Actinium was discovered by A. Debierne in 1899 in Paris, France. Appearance Actinium is a soft, silvery-white metal which glows in the dark. Source Actinium occurs naturally in uranium minerals. It is made by the neutron bombardment of the radium isotope 226Ra. Uses Actinium is a very powerful source of alpha rays, but is rarely used outside research. Biological Role Actinium has no known biological role. It is toxic due to its radioactivity. General Information Actinium reacts with water to evolve hydrogen gas. Its chemical properties have been little studied.

	Physical Information
	Atomic Number		89
	Relative Atomic Mass (12C=12.000)		227 (radioactive)
	Melting Point/K		1320
	Boiling Point/K		3470
	Density/kg m-3		10060 (293K)
	Ground State Electron Configuration		[Rn]6d17s2

	Key Isotopes
	nuclide	225Ac	227Ac	228Ac
	atomic mass		227.03
	natural abundance	0%	trace	trace
	half-life	10 days	21.6 yrs	6.13 h

Other Information
Enthalpy of Fusion/kJ mol-1		14.2
Enthalpy of Vaporisation/kJ mol-1		293
Oxidation States
AcO, Ac+3

	Ionisation Energies/kJ mol-1
	M - M+	499
	M+ - M2+	1170
	M2+ - M3+	1900
	M3+ - M4+	4700
	M4+ - M5+	6000
	M5+ - M6+	7300
	M6+ - M7+	9200
	M7+ - M8+	10500
	M8+ - M9+	11900
	M9+ - M10+	15800