34
Se
selenium
78.971

General properties

Group
group 16 (chalcogens)
Period
period 4
Category
nonmetals
Standard atomic weight
78.971(8)
Melting point
494 K (221 °C)
Boiling point
958 K (685 °C)
Phase at STP
solid

Additional properties

Block
p-block
Electron configuration
[Ar] 3d¹⁰ 4s² 4p⁴
Electrons per shell
2, 8, 18, 6
Electronegativity
2.55
Density
gray: 4.81 g/cm³ alpha: 4.39 g/cm³ vitreous: 4.28 g/cm³
Oxidation states
−2, −1, +1, +2, +3, +4, +5, +6 (a strongly oxide)
CAS Number
7782-49-2