Noble gas compound

Noble gas compounds are chemical compounds that include an element from the noble gases, group 18 of the periodic table. Although the noble gases are generally unreactive elements, many such compounds have been observed, particularly involving the element xenon. From the standpoint of chemistry, the noble gases may be divided into two groups: the relatively reactive krypton (ionisation energy 14.0 eV), xenon (12.1 eV), and radon (10.7 eV) on one side, and the very unreactive argon (15.8 eV), neon (21.6 eV), and helium (24.6 eV) on the other.

It was initially believed that the noble gases could not form compounds due to their full valence shell of electrons that rendered them very chemically stable and nonreactive.

All noble gases have full s and p outer electron shells (except helium, which has no p sublevel), and so do not form chemical compounds easily. Because of their high ionization energy and almost zero electron affinity, they were not expected to be reactive.

In 1933, Linus Pauling predicted that the heavier noble gases would be able to form compounds with fluorine and oxygen. Specifically, he predicted the existence of krypton hexafluoride (KrF₆) and xenon hexafluoride (XeF₆), speculated that XeF₈ might exist as an unstable compound, and suggested that xenic acid would form perxenate salts. These predictions proved quite accurate, although subsequent predictions for XeF₈ indicated that it would be not only thermodynamically unstable, but kinematically unstable. As of 2013, XeF₈ has not been made, although the octafluoroxenate(VI) anion (XeF2−
8) has been observed.

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