selenium

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Symbol:

Se

Atomic Number:

34

Relative Atomic Mass:

78.96 g mol^-1

Natural Abundance in Lithosphere, hydrosphere and atmosphere:

8 x 10^-5% (mass fraction)

Electron Configuration:

[Ar]3d¹⁰4s²4p⁴

Oxidation States:

VI, IV, -II

Atomic Radius:

116pm

Covalent Radius:

117pm

Ionic Radius:

50pm (for +4 oxidation state)

198pm (for -2 oxidation state)

Melting Point:

221°C

Density:

4.19 g cm^-3 (at 20°C)

First Ionisation Energy:

9.752 eV

Reduction Potential:

-0.924V

for Se + 2e^- a Se^2-

Electronegativity (Allred and Rochow):

2.5

Number of Natural Isotopes:

6

Mass Number of the Most Abundant Isotopes:

76 g mol^-1 a 9.4% abundance

78 g mol^-1 a 23.8% abundance

80 g mol^-1 a 49.6% abundance