Argon is the third most abundant gas in the atmosphere, after nitrogen and oxygen. It does not react with any other element and is named after the Greek word argos, meaning inactive. Argon is not a good conductor of heat, so it is placed in double-glazed windows and used in diving suits during deep, cold dives. Its lack of reactivity is useful. Argon is used in museums to protect delicate works of art. It also stops the reaction of metals during hot welding. This element is also useful in titanium production.

Summary of properties (Ar)

Atomic weight39.948(1)
Discoverer (year)Ramsay, Sir William & Strutt, John (1894)
Natural formgas
Electron configuration[Ne] 3s2 3p6
Melting point (ºC)-189
Boiling point (ºC)-186
Abundance in earth's crust (ppm)3.5
Isotope (abundance)36Ar (0.3365), 38Ar (0.0632), 40Ar (99.6003)
Density g/cm30.86
Van der Waals radius (pm)188
Covalent radius (pm)101
Electronegativity (Pauling)
Vaporization enthalpy (kJ/mol)6.43
Enthalpy of fusion (kJ/mol)1.18
Specific heat capacity (J/g·K) at 25ºC and 1 atm0.52
Thermal conductivity (W/cm·K) at 25ºC and 1 atm<0.001
Oxidation state0
Electron affinity (eV)unstable ion
1st Ionization potential (eV)15.7596

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