Relative atomic mass: 231.03588 +- 0.00002

English: Protactinium
French: Protactinium
Croatian: Protaktinij
German: Protactinium
Italian: Protoattinio
Spanish: Protactinio

Atomic number: 91
Group numbers: 3
Period: 7
Standard state (20 oC): solid

Discovery: 1913 Kasimir Fajans, Otto H. Gohring (DE)
Protactinium was discovered by Kasimir Fajans and Otto H. Gohring (DE) in 1913. The origin of the name comes from the Greek word protos meaning first. It is a very rare, silvery-white, extremely radioactive metal that resists alkalis, reacts with oxygen, acids and steam. Protactinium is highly radiotoxic, extremely toxic and must be handled with great care. Protactinium does not occur in nature. It is found among fission products of uranium, thorium and plutonium.
Electronic configuration: [Rn] 5f2 6d1 7s2
Formal oxidation number: +4 +5
Atomic radius: 156.1 pm

Electronegativities: 1.5
Thermal conductivity: 47 W/(m K)
Electrical resistivity (20 oC): 19.1 microOhm cm

Melting point: 1572 oC
Boiling point: - oC

Heat of fusion: 16.7 kJ/mol
Heat of vaporization: 481 kJ/mol
Heat of atomization: 607 kJ/mol

90Th <= 91Pa => 92U

ASCII Periodic Table of the Elements
29 Aug. 2017
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