Selenium

Document v1 · published by Koskamo · updated 2026-10-04

Selenium (Se) is chemical element 34, a nonmetal in group 16, period 4 (PubChem).

Atomic number: 34
Symbol: Se
Group: 16
Period: 4
Atomic mass: 78.97 u
Electron configuration: [Ar]4s2 3d10 4p4
Electronegativity (Pauling scale): 2.55
Atomic radius (van der Waals): 190 pm
Ionization energy: 9.752 eV
Electron affinity: 2.021 eV
Oxidation states: +6, +4, -2
Standard state: Solid
Melting point: 493.65 K
Boiling point: 958 K
Density: 4.809 g/cm³
Chemical group: Nonmetal
Year discovered: 1817

Source and provenance

Original source: pubchem.ncbi.nlm.nih.gov
Published on Koskamo by: Koskamo
Citation version: Document v1
Reuse: PubChem periodic table data (NIH/NLM, pubchem.ncbi.nlm.nih.gov/ptable); group and period from Jefferson Lab via PubChem

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Version history

Published by Koskamo2026-10-04
Version 1