Argon (Ar)

Argon is a chemical element with symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas.

Atomic Number

18

Atomic Mass

39.948 u

Category

noble gas

Phase

gas

Density

0.0017837 g/cm³

Electron Shells

2, 8, 8

Atomic Structure

Protons: 18 • Electrons: 18 • Neutrons: Varies by isotope

Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶

Discovery

1894 • Lord Rayleigh, William Ramsay