Selenium

Atomic number

34

Atomic mass (u)

78.97

Category

Nonmetal

Standard state

Solid

Melting point

220.5 °C (493.65 K)

Boiling point

684.85 °C (958 K)

Density (g/cm³)

4.809

Electronegativity (Pauling)

2.55

Electron configuration

[Ar]4s2 3d10 4p4

Oxidation states

+6, +4, -2

Atomic radius (pm)

190

First ionization energy (eV)

9.752

Discovery & recognition

Discovery year / period (PubChem)

1817

Discovery credited to (RSC)

Jöns Jacob Berzelius

Date or period recorded by RSC

1817

Discovery place

Not supplied in the structured record; see the RSC history source.

An ancient date does not identify a first human discovery. Different references may date observation, isolation and formal recognition differently.

Natural occurrence & production

The creation of an element’s nuclei and its concentration into terrestrial deposits are different processes. The occurrence note below concerns its presence or production on Earth; it is not a complete account of nucleosynthesis.

“Selenium is found in a few rare minerals.”

Royal Society of Chemistry · occurrence excerpt ↗

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Reference values are not product specifications. Blank values have not been estimated. For superheavy elements, some properties and family assignments are theoretical or incompletely measured.