protactinium

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Symbol:

Pa

Atomic Number:

91

Relative Atomic Mass:

231.03588 g mol^-1

Natural Abundance in Lithosphere, hydrosphere and atmosphere:

9 x 10^-11% (mass fraction)

Electron Configuration:

[Rn]5f²6d7s²

Oxidation States:

V, IV

Atomic Radius:

156.1pm

Ionic Radius:

78pm (for +5 oxidation state)

Melting Point:

1554°C

Density:

15.37 g cm^-3 (at 20°C)

Reduction Potential:

-1.49V

for Pa³⁺ + 3e^- a Pa_(s)

Electronegativity (Allred and Rochow):

1.1

Number of Natural Isotopes:

2

Mass Number of the Most Abundant Isotopes:

231 g mol^-1 a ~100% abundance

234 g mol^-1 a ~10^-9% abundance