Xenon

Xenon was discovered in 1898 by William Ramsay and Morris Travers, the last of the stable noble gases they extracted from liquefied air, present only in the barest trace. Its name comes from the Greek xenos, stranger or foreigner. Xenon is a heavy, colourless, odourless gas, used in bright arc lamps and as a surprisingly effective general anaesthetic. Rare and costly, xenon lights bright arc and camera-flash lamps, drives the ion thrusters that propel some spacecraft, and serves in medical imaging, while its short-lived radioactive isotopes are watched for as telltale signs of nuclear reactions and explosions.

Xenon's anaesthetic property, discovered in the 1940s and confirmed clinically only decades later, makes it one of the safest general anaesthetics known, since it produces almost none of the cardiovascular side effects of conventional agents, though its high cost and scarcity have kept it a niche option used mainly in specialist and research settings rather than routine surgery. In fundamental physics, tanks of ultra-pure liquid xenon are now the leading medium for experiments such as XENON1T and LUX-ZEPLIN, which sit deep underground hoping to catch the faint recoil of a hypothetical dark-matter particle striking a xenon nucleus, placing this once merely rare gas at the frontier of the search for the universe's missing mass.

Named the stranger for its rarity and for how thoroughly it had hidden in the air, xenon later overturned one of chemistry's confident beliefs. The noble gases had been held to be utterly inert, incapable of forming compounds at all, a dogma so firm it appeared in textbooks as settled fact. In 1962 the chemist Neil Bartlett showed that xenon would react with the powerful oxidiser platinum hexafluoride to form a genuine compound, and a family of xenon fluorides and oxides soon followed. The stranger thus proved the least inert of the inert gases and forced a rewriting of the rules of bonding. Xenon has no ancient tradition, but its story carries the lesson that even a name meaning outsider could not keep it forever aloof.

Bartlett's insight came from an unrelated observation: he had just shown that platinum hexafluoride was powerful enough to oxidise ordinary oxygen gas, and, noticing that xenon's first ionisation energy was almost identical to that of molecular oxygen, reasoned that if PtF6 could strip an electron from O2 it ought to do the same to xenon, a chain of reasoning that led directly to the compound now known as xenon hexafluoroplatinate. Later reanalysis showed his original product was actually a more complex mixture of xenon-platinum-fluorine compounds, but the central chemical fact, that a noble gas could be made to bond, stood, and it triggered a wave of noble-gas chemistry that within a year produced krypton and radon compounds too.