The Case of the Missing Xenon
Xenon is the second heaviest of the Noble gases. The lighter ones—neon, argon, and krypton—are all present in the atmosphere at about the level expected from predictions of primordial concentration. Big old xenon, though, is missing in action, with about 90% unaccounted for.
Where did the misplaced xenon go? Previous attempts at explanations include xenon entrapment in water, ice, or sediments, or possibly escape from the atmosphere into space. All have proven untenable.
A report by two chemists at McMaster University seems to solve the puzzle (Journal of the American Chemical Society [February 22, 2011], doi:10.1021/ja110618g). The new work posits that XeO2 could substitute for SiO2 in the silicate materials of the earth’s crust, which of course is a huge potential reservoir.
The problem is that XeO2 had not been known to exist. The authors remedied that problem by creating a straightforward synthetic route to XeO2, which turns out to be a beautiful yellow color. Wonderfully, the geometry of the new compound is square planar, which fits perfectly in SiO2 lattices. And adding to the wonder, XeO2 is the only known covalent network structure for a noble gas compound that exists at near ambient conditions.
Now all we have to do to close the case is search the earth’s crust for all that missing xenon. Sounds like a good research project for an enterprising chemical explorer.