Xenon

About Xenon

Xenon is the noble gas that stopped being noble. For sixty years after Ramsay and Travers fractionated it from the dregs of liquid air in 1898, every textbook called the group 18 elements chemically inert. Then in 1962 Neil Bartlett noticed that PtF₆ oxidized O₂ to O₂⁺[PtF₆]⁻, calculated that xenon's first ionization energy was actually lower than O₂'s, mixed the two gases, and got a yellow-orange solid. The field of noble gas chemistry started that afternoon. Xenon now has a respectable coordination chemistry built around fluorides — XeF₂, XeF₄, XeF₆ — and the powerful oxidizers XeO₃ and XeO₄. The element is rare enough (87 ppb in the atmosphere) that recovering a kilogram requires processing roughly ten million cubic meters of air, which is why it costs around $10 per liter at STP. That cost is justified for the applications that nothing else does: xenon arc lamps put out the closest thing to a continuous solar spectrum we can make in a tube, and Hall-effect thrusters on satellites ionize xenon to push payloads with specific impulses around 1,500 seconds.