Xenon was discovered by Ramsay and Travers in 1898 in the residue left after evaporating liquid air components. It is present in the atmosphere to the extent of about one part in twenty million. The element is found in the gases evolved from certain mineral springs, and is commercially obtained by extraction from liquid air.
Natural xenon is composed of nine stable isotopes.
Until recently, xenon has been considered inert and unable to form compounds with other elements. Those compounds that were occasionally reported in the literature were considered not to be true compounds. Evidence has been mounting in the past few years that xenon, as well as other members of the zero valence elements, do form compounds. More recently, xenon trioxide, which is highly explosive, has been prepared. The structure of these substances is still open to question.