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Periodic table / Other non-metals

34Selenium

Selenium is an other non-metal in group 16, period 4. At 25 °C it is a solid.

Se
Shells: 2, 8, 18, 6. A simple picture: electrons do not move in circles.
Symbol
Se
Atomic number
34 protons in the nucleus
Standard atomic weight
78.971 ± 0.008The isotope mix varies in normal samples, so the value cannot be given more precisely.
Electron configuration
[Ar] 3d10 4s2 4p4
Electrons in each shell
2, 8, 18, 6
Group, period, block
16, 4, p
Family
Other non-metals
State at 25 °C
solid
Electronegativity
2.55 (Pauling scale)
First ionisation energy
941 kJ/mol (9.752368 eV)
Where these numbers come from

Atomic weight: IUPAC CIAAW, abridged standard atomic weights 2024. Electron configuration and ionisation energy: NIST Atomic Spectra Database. Family, state and electronegativity: PubChem. See Sources. Melting points, boiling points and densities are left out for now: published values differ between sources, and we will add them once each has been checked.