Selenium (Se)

Selenium is a chemical element with symbol Se and atomic number 34. It is a nonmetal with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium.

Atomic Number

34

Atomic Mass

78.971 u

Category

nonmetal

Phase

solid

Density

4.81 g/cm³

Electron Shells

2, 8, 18, 6

Atomic Structure

Protons: 34 • Electrons: 34 • Neutrons: Varies by isotope

Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴

Discovery

1817 • Jöns Jakob Berzelius