Protactinium (atomic symbol "Pa", atomic number = 91, atomic weight = 231.0359) is a radioactive rare earth metal, one of the rarest naturally-occurring elements. It is an alpha emitter and requires precautions while handling.

Symbol: Pa
Atomic Number: 91
Atomic Weight: 231.0359
Boiling Point: 4300 K
Melting Point: 1845 K
Density at 300K: 15.4 g/cm3
Covalent radius: ???
Atomic radius: ???
Atomic volume: 15.0 cm3/mol
First ionization potental: 5.88 V
Specific heat capacity: ??? Jg-1K-1
Thermal conductivity: 47 Wm-1K-1
Electrical conductivity: 5.6*106Ω-1m-1
Heat of fusion: ??? kJ/mol
Heat of vaporization: ??? kJ/mol
Electronegativity: 1.5 (Pauling's)

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