Oxygen (O)

Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a highly reactive nonmetal.

Atomic Number

8

Atomic Mass

15.999 u

Category

nonmetal

Phase

gas

Density

0.001429 g/cm³

Electron Shells

2, 6

Atomic Structure

Protons: 8 • Electrons: 8 • Neutrons: Varies by isotope

Electron Configuration: 1s² 2s² 2p⁴

Discovery

1771 • Carl Wilhelm Scheele