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Argon - Ar General Information Discovery Argon was discovered in 1894 by Lord Rayleigh and Sir William Ramsey in the UK, although the presence of an inert component in air was suspected by Cavendish in 1785. Appearance Argon is a colourless, odourless gas. Source The atmosphere contains 0.94% argon. It is obtained commercially from liquid air. Uses Argon is used in electric light bulbs and fluorescent tubes at a pressure of about 3 mm. Industrially, it is used as an inert gas shield for arc welding, and as a blanket for the production of titanium and other reactive elements. Biological Role Argon has no known biological role. General Information Argon is considered to be a very inert gas and does not form true compounds as do others in the same Group. However, it does form clathrates with water and quinol in which the argon atoms are trapped inside a lattice of the other molecules. |
| Physical Information | |||
| Atomic Number | 18 | ||
| Relative Atomic Mass (12C=12.000) | 39.948 | ||
| Melting Point/K | 84 | ||
| Boiling Point/K | 87 | ||
| Density/kg m-3 | 1.783 (273K) | ||
| Ground State Electron Configuration | [Ne]3s23p6 | ||
| Electron Affinity(M-M-)/kJ mol-1 | +35 (calc) |
| Key Isotopes | ||||||
| nuclide | 36Ar | 37Ar | 38Ar | 39Ar | 40Ar | |
| atomic mass | 35.968 | 36.967 | 37.963 | 38.964 | 39.962 | |
| natural abundance | 0.337% | 0% | 0.063% | 0% | 99.6% | |
| half-life | stable | 35 days | stable | 269 yrs | stable |
| Other Information | ||
| Enthalpy of Fusion/kJ mol-1 | 1.21 | |
| Enthalpy of Vaporisation/kJ mol-1 | 6.53 | |
| Oxidation States | ||
| Ar0 | ||
| Ionisation Energies/kJ mol-1 | ||
| M - M+ | 1520.4 | |
| M+ - M2+ | 2665.2 | |
| M2+ - M3+ | 3928 | |
| M3+ - M4+ | 5770 | |
| M4+ - M5+ | 7238 | |
| M5+ - M6+ | 8811 | |
| M6+ - M7+ | 12021 | |
| M7+ - M8+ | 13844 | |
| M8+ - M9+ | 40759 | |
| M9+ - M10+ | 46186 | |
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