Selenium

Nonmetal · 78.97 u · group 16, period 4

Selenium · Se

Atomic number34

SymbolSe

CategoryNonmetal

Standard stateSolid

Group · Period · Block16 · 4 · p

Electron configuration[Ar]4s2 3d10 4p4

Atomic mass78.97 u

Atomic radius190 pm

Protons / Neutrons / Electrons34 / 45 / 34

Shells (e⁻ per shell)2, 8, 18, 6

Electronegativity (Pauling)2.55

Ionization energy9.752 eV

Electron affinity2.021 eV

Oxidation states+6, +4, -2

Melting point493.6 K · 220.5 °C

Boiling point958 K · 684.9 °C

Density4.809 g/cm³

Year discovered1817

CPK color

#FFA100

State at room temp (25 °C)

solid

Position

1 in library