Argon is a colourless and odourless gas present to a very small extent in the atmosphere. Argon is very inert (indeed it is referred to as one of the noble gases) and is not known to form true chemical compounds. It makes a good atmosphere for working with air-sensitive materials since it is heavier than air and less reactive than N2. Today, the chemical symbol for argon is Ar but until 1957 its sybol was simply A.
Image adapted with permission fromProf James Marshall's (U. North Texas, USA)Walking Tour of the elements CD.
Argon wasdiscovered by Sir William Ramsay, Lord Rayleigh in 1894 at UCL, London, England.Origin of name: from the Greek word "argos" meaning "inactive".
Isotope abundances of argon with the most intense signal set to 100%.
Argon isotopes are used as precursors in the production of radioisotopes. Ar-40 and Ar-38 are used in the production of radioactive K-38 which can be used as a blood flow tracer. Ar-40 is used in the production of radioactive Ar-41 which is used to trace gas flows.
Isolation: argon is present to a small extent in the atmosphere and is obtained as a byproduct from the liquefaction and separation of air. This would not normally be carried out in the laboratory and argon is available commercially in cylinders at high pressure.
Density of solid: 1616 kg m-3
Molar volume: 22.56 cm3
Thermal conductivity: 0.01772 W m‑1 K‑1
Melting point: 83.8 [‑189.3 °C (‑308.7 °F)] K
Boiling point: 87.3 [‑185.8 °C (‑302.4 °F)] K
Enthalpy of fusion: 20.5 kJ mol-1
Atomic radius (empirical): (no data) pm
Molecular single bond covalent radius: 96 (coordination number 1,2) ppm
van der Waals radius: 183 ppm
Pauling electronegativity: (no data) (Pauling units)
Allred Rochow electronegativity: 3.20 (Pauling units)
Mulliken-Jaffe electronegativity: 3.19 (12.5% s orbital)
First ionisation energy: 1520.57 kJ mol‑1
Second ionisation energy: 2665.86 kJ mol‑1
Third ionisation energy: 3930 kJ mol‑1
Universe: 200000 ppb by weight
Crustal rocks: 1500 ppb by weight
Human: (no data) ppb by weight
