Protactinium - Pa General Information Discovery Protactinium was discovered in 1917 by Hahn and Meitner in Berlin, Fajans in Germany and Fleck in Glasgow. It was initially named brevium, as the first isotope identified was very short-lived. Appearance Protactinium is a radioactive, silvery metal. Source Protactinium is found naturally in uranium ores and produced in gram quantities from uranium fuel elements. Uses Protactinium is little used. Biological Role Protactinium has no known biological role. It is toxic due to its radioactivity. General Information Protactinium is attacked by oxygen, steam and acids, but not by alkalis. It is the third rarest of the natural elements.

	Physical Information
	Atomic Number		91
	Relative Atomic Mass (12C=12.000)		231.04
	Melting Point/K		2113
	Boiling Point/K		4300
	Ground State Electron Configuration		[Rn]5f26d17s2

	Key Isotopes
	nuclide	231Pa	233Pa	234Pa
	atomic mass	231.04	233.04	234.04
	natural abundance	trace	0%	trace
	half-life	3.26x104 yrs	27 days	6.75 h

Other Information
Enthalpy of Fusion/kJ mol-1		16.7
Enthalpy of Vaporisation/kJ mol-1		481
Oxidation States
main	Pa+5
others	Pa+3, Pa+4

	Ionisation Energies/kJ mol-1
	M - M+	568
	M+ - M2+
	M2+ - M3+
	M3+ - M4+
	M4+ - M5+
	M5+ - M6+
	M6+ - M7+
	M7+ - M8+
	M8+ - M9+
	M9+ - M10+