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Helium’s inertness defied by high-pressure compound

Crushing elements together with diamonds creates a rare mash-up

9:00am, February 17, 2017
helium sodium compound

HELIUM COMPOUND  Scientists created a chemical compound of helium and sodium by squeezing the elements to extremely high pressures. Helium atoms (green cubes) are arranged in a 3-D checkerboard structure, each surrounded by eight sodium atoms (purple). Electron pairs (red) sit in the spaces between helium atoms.

Helium — the recluse of the periodic table — is reluctant to react with other elements. But squeeze the element hard enough, and it will form a chemical compound with sodium, scientists report.

Helium, a noble gas, is one of the periodic table’s least reactive elements. Originally, the noble gases were believed incapable of forming any chemical compounds at all. But after scientists created xenon compounds in the early 1960s, a slew of other noble gas compounds followed. Helium, however, has largely been a holdout.

Although helium was known to hook up with certain elements, the bonds in those compounds were weak, or the compounds were short-lived or electrically charged. But the new compound, called sodium helide or Na2He, is stable at high pressure, and its bonds are strong, an international team of scientists reports February 6 in Nature Chemistry.

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