Template:Infobox protactinium

Protactinium,  ₉₁Pa

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General properties
Pronunciation	Template:Infobox element/pronunciation
Appearance	bright, silvery metallic luster
Standard atomic weight (Ar, standard)	Template:Infobox element/standard atomic weight
Mass number	Template:Infobox element/symbol-to-most-stable-isotope (most stable isotope)
Protactinium in the periodic table
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Atomic number (Z)	91
Group	Template:Infobox element/group
Period	period 7
Block	f-block
Element category	Template:Infobox element/category format
Electron configuration	[Rn] 5f2 6d1 7s2
Electrons per shell	2, 8, 18, 32, 20, 9, 2
Physical properties
Phase at STP	solid
Melting point	1841 K ​(1568 °C, ​2854 °F)
Boiling point	4300 K ​(4027 °C, ​7280 °F) (?)
Density (near r.t.)	15.37 g/cm3
Heat of fusion	12.34 kJ/mol
[[Enthalpy of vaporization|Heat of Template:Engvar]]	481 kJ/mol
Atomic properties
Oxidation states	Template:Infobox element/symbol-to-oxidation-state
Electronegativity	Pauling scale: 1.5
[[Ionization energy|Template:Engvar energies]]	1st: 568 kJ/mol
Atomic radius	empirical: 163 pm
Covalent radius	200 pm
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Other properties
Crystal structure	​Template:Infobox element/crystal structure Template:Infobox element/crystal structure
Thermal expansion	~9.9 µm/(m·K) (at r.t.)
Thermal conductivity	47 W/(m·K)
Electrical resistivity	177 nΩ·m (at 0 °C)
Magnetic ordering	paramagnetic
CAS Number	7440-13-3
History
Prediction	Dmitri Mendeleev (1869)
Discovery and first isolation	Kasimir Fajans and Oswald Helmuth Göhring (1913)
Named by	Otto Hahn and Lise Meitner (1917–8)
Main isotopes of protactinium
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