Xenon is a member of the zero-valence elements that are called noble or inert gases. The word "inert" is no longer used to describe this chemical series since some zero valence elements do form compounds. In a gas filled tube, xenon emits a beautiful blue glow when the gas is excited by electrical discharge. Using several hundred kilobars of pressure metallic xenon has been made. Xenon can also form clathrates with water when atoms of it are trapped in a lattice of the water molecules.
Xenon (Greekxenon meaning "stranger") was discovered by William Ramsay and Morris Travers in 1898 in the residue left over from evaporating components of liquid air.
It is a trace gas in Earth's atmosphere, occurring in one part in twenty million. The element is obtained commercially through extraction from the residues of liquefied air. This noble gas is naturally found in gases emitted from some mineral springs. Xe-133 and Xe-135 are synthesized by neutron irradiation within air-cooled nuclear reactors.
Naturally occurring xenon is made of eight stable and one slightly radioactiveisotopes. Beyond these stable forms, there are 20 unstable isotopes that have been studied. Xe-129 is produced by beta decay of I-129 (half-life: 16 million years); Xe-131, Xe-132, Xe-134 and Xe-136 are fission products of both U-238 and Pu-244. Because Xe is a tracer for two parent isotopes, Xe isotope ratios in meteorites are a powerful tool for studying the formation of the solar system. The I-Xe method of dating gives the time elapsed between nucleosynthesis and the condensation of a solid object from the solar nebula. Xenon isotopes are also a powerful tool for understanding terrestrial differentiation. Excess Xe-129 found in carbon dioxide well gases from New Mexico was believed to be from the decay of mantle-derived gases soon after Earth's formation.
