Xenon, derived from the Greek word xenos, meaning stranger, is present in the air in minute quantities. Although sources disagree on the exact atmospheric abundance, it is believed to be as little as 0.08parts per million. It has an atomic mass of 131.29 and an atomic radius of 1.24 Angstrom.

Sir William Ramsay discovered xenon in 1898. Until 1962, noble gases were believed to be inert. This was found to be an incorrect analogy by the British chemist Neil Bartlett, who successfully made the first noble gas compound, xenon hexafluoroplatinate (vi). Since this discovery, over 80 compounds of xenon have been made. Some of the compounds are particularly important due to their strong oxidising powers.

Apart from Radon, which because of its short half-life has hardly been studied, xenon has the lowest first ionisation energy of all other noble gases. This explains why it is found to form more noble gas compounds than any other member of group 18. Common compounds include XeF₂ XeF₄, XeF₆, and XeO₃. VSEPR can be used to calculate the shapes of such compounds. For example, the shape of XeF₄ can be predicted by this method. Xenon's outer electron structure is 5s²5p⁶. This corresponds to eight electrons in its outer shell. The four fluorine atoms add four more electrons to the outer shell resulting in the xenon atom having six electron pairs. The compound is therefore octahedral.

Xenon, like all other noble gases, is colourless, odourless, and tasteless. It has a melting point of 161.36K and a boiling point of 165.03K. Xenon is used for filling flash lamps and is especially used in high-speed photographic tubes. It is also used in bubble chambers.

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