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Element Fact
Rhenium was the last naturally occurring element to be identified, in 1925. It was so rare that only 1 g of the metal was extracted out of 660 kg of molybdenite ore.

Xenon, Xe

xenon sample

Atomic number: 54
Atomic mass: 131.293(6)
Natural abundance: -
124Xe (123.905896) - 0.10%
126Xe (125.904269) - 0.09%
128Xe (127.903530) - 1.91%
129Xe (129.9047794) - 26.4%
130Xe (129.903508) - 4.1%
131Xe (130.905082) - 21.2%
132Xe (131.904154) - 26.9%
134Xe (133.905394) - 10.4%
136Xe (135.907220) - 8.9%

History and Production

Derived from Greek xenon, meaning stranger. The gas was discovered by W. Ramsey and M.W. Travers in 1898 by the low temperature distillation of liquid air. The commercial source can be obtained by fractional distillation of air. It is used to make stroboscopic lamps, excitation of ruby lasers and also discharge tubes which give a blue glow.

Physical Data

It is colorless, odorless gas. Due to its inert nature the gas is found in its elemental form in air (0.087 ppm by volume).

Interatomic distance: 420 pm (van der Waals)
Melting point: -111.79C
Boiling point: -108.12C
Thermal conductivity/Wm-1K-1: 0.00569 (27C)
Density/kgm-3: 3540 (m.p.), 2939 (b.p.), 5.8971 (0C)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 0.0 kJ/mol
Gibbs free energy of formation: -
Entropy: 169.7 J/mol K
Heat capacity: 20.8 J/mol K

Electronic data

Electronic configuration: [Kr] 4d10 5s2 5p6 = [Xe]
Term symbol: 1S0
Electron affinity: not stable   Electronegativity (Pauline): 2.60
Ionization energy (first, second, third): 1170.35, 2046.44, 3099.40 kJ/mol

Chemical properties

It is the most 'reactive' among the inert gas members. A variety of compounds such as oxides, fluorides (XeF4, XeF2) metal complexes (XePtF6, XeRhF6) have been prepared in the laboratory. most of these compounds are unstable (though more stable than other lighter noble gas counterparts) and strong oxidizing characteristics.

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