Periodic Table of Elements




Selenium was discovered by Swedish chemists Jns Jacob Berzelius and Johan Gottlieb Gahn in 1817 after analyzing an red precipitate that was contaminating the sulfuric acid (H2SO4) being produced at a chemistry plant in Sweden. Berzelius named the new element after the Moon.

Name: Selenium
Symbol: Se
Atomic number: 34
Atomic weight: 78.96
State: solid
Group, period, block: 16, 4, p
Color: black and red allotropes
Classification: Non-metallic
Electron configuration: 3d10 4s2 4p4

Physical properties

Density: (gray) 4.81 g/cm-3
Melting point: 494 K,221 C,430 F
Boiling point: 958 K,685 C,1265 F

Atomic properties

Oxidation states: 6, 4, 2, 1,[1] -2
Electronegativity: 2.55 (Pauling scale)
Ionization energies: 1st: 941.0 kJmol-1
Covalent radius: 1204 pm
Van der Waals radius: 190 pm
  • Se
  • Electron Configuration


There are six naturally occurring isotopes of selenium exist, 74Se, 76Se, 77Se, 78Se, 80Se, and 82Se.