Helium is a famously inert element, but researchers have made a stable compound from helium and sodium.

Artem Oganov at Stony Brook University in New York and his colleagues used an algorithm to look for potentially stable helium compounds and predicted that Na2He could be made. They demonstrated this experimentally by subjecting thin pieces of sodium and helium gas to high pressures of up to 155 gigapascals. Above 113 GPa, the team noticed the formation of a stable crystalline compound, Na2He, that is expected to remain stable up to at least 1,000 GPa. The crystal structure contains cubes of eight sodium atoms; half of these are filled with helium atoms, and the other half are each occupied by an electron pair, binding the sodium atoms together.

The finding could have implications for the understanding of noble gases, chemical bonding and giant gas planets such as Jupiter, which contain high levels of helium.

Nature Chem. http://doi.org/bzkz (2017)