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.
Atomic number: 18
Atomic weight: 39.948
Group, period, block: 18, 3, p
Classification: noble gases
Electron configuration: 3s2 3p6
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
Oxidation states: 2, 1, 0
Electronegativity: no data (Pauling scale)
Ionization energies: 1st: 1520.6 kJ·mol-1
Covalent radius: 106±10 pm
Van der Waals radius: 188 pm
There are three naturally occurring isotopes of argon exist, 36Ar, 38Ar and 40Ar.