Arsenic Bromine

Selenium (Se)

From Wikipedia, the free encyclopediaSelenium is a chemical element with symbol Se and atomic number 34. It is a nonmetal with properties that are intermediate between those of its periodic table column-adjacent chalcogen elements sulfur and tellurium. It rarely occurs in its elemental state in nature, or as pure ore compounds.

Selenium in the periodic table

Symbol

Atomic number

Group

Period

Block

Element category

Nonmetal

Physical properties

Phase at STP

Solid

Density

4.81 g/cm³

Atomic weight

78.9718 u

Melting point

494 K
220.85 °C
429.53 °F

Boiling point

958 K
684.85 °C
1264.73 °F

Atomic properties

Electronegativity (Pauling Scale)

2.55

Electron affinity

194.959 kJ/mol

Oxidation states

−2, −1, +1, +2, +3, +4, +5, +6
(a strongly acidic oxide)

Ionization energies

1	941 kJ/mol
2	2045 kJ/mol
3	2973.7 kJ/mol
4	4144 kJ/mol
5	6590 kJ/mol
6	7880 kJ/mol
7	14990 kJ/mol

Electron configuration

Elektronkonfiguration (shorthand)

[Ar] 3d¹⁰ 4s² 4p⁴

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴

Electrons per shell

2, 8, 18, 6

History

Discovered

1817

Discovered by

Jöns Jakob Berzelius
Johan Gottlieb Gahn