Periodic Table of Elements




Argon was the first noble gas to be discovered. Argon was suspected to be present in air by Henry Cavendish in 1785. But it was discovered in 1894 by Lord Rayleigh and Sir William Ramsay.

Name: argon
Symbol: Ar
Atomic number: 18
Atomic weight: 39.948
State: gas
Group, period, block: 18, 3, p
Color: colorless
Classification: noble gases
Electron configuration: 3s2 3p6

Physical properties

Density @293 K: 1.784 g/cm3
Melting point: 83.80 K, -189.35 C, -308.83 F
Boiling point: 87.30 K, -185.85 C, -302.53 F

Atomic properties

Oxidation states: 2, 1, 0
Electronegativity: no data (Pauling scale)
Ionization energies: 1st: 1520.6 kJmol-1
Covalent radius: 10610 pm
Van der Waals radius: 188 pm
  • Ar
  • Electron Configuration


There are three naturally occurring isotopes of argon exist, 36Ar, 38Ar and 40Ar.