Helium has long been considered a noble gas, and like nobility, it isn’t known for mixing in with ‘commoners’ such as oxygen, carbon or any other element for that matter.
But now, new research published in the journal Nature Communications has revealed helium is capable of forming stable compounds under the right conditions. The discovery suggests that there may be much more helium in the Earth’s mantle than previously thought, which is great news considering helium has many important uses, and our supply of it is dwindling.
The researchers behind the new study said their work was influenced by a 2017 study, from another research group, on the synthesis of a stable compound from helium and sodium under high-pressure conditions. The team behind the latest study said they wanted to find out how the creation of a stable helium compound was possible; they discovered it was because helium acted as a mediator for charged compounds.
“We propose that there is a general driving force for helium to react with ionic compounds as soon as these compounds have unequal numbers of negatively charged and positively charged ions,” study author Maosheng Miao, a chemistry professor at California State University, Northridge (CSUN), said in a news release. “As a result, it stabilizes what would normally be an unstable situation, sort of the way a nanny mediates when your kids don’t get along.”
Ions are atoms or molecules with a positive or negative electric charge. In many stable compounds, one negatively-charged ion is balanced out by a positively-charged ion. For example, water is stable compound comprised of a single oxygen ion with two negative charges and two positively-charged hydrogen ions.
However, when compounds consist of unequal quantities of negatively and positively-charged ions, repulsive forces between atoms of the same charge may cause instability. The new study found helium can act as a sort of ‘nanny’ that maintains a sense of order for these charged compounds in high-pressure conditions.
You know what happens when you force your kids to sit together in the back seat of a small car, sometimes they don’t get along - there’s bickering and pushing. Well, helium is the nanny in this chemical compound’s car. It sits between the kids to help them get along, but it really isn’t part of the family.
With regard to chemical compounds, helium doesn’t develop any type of chemical bond with its nearby atoms. On the other hand, it positions itself between the compound’s charged ions to keep them stable.
The study team said their study lays the foundation for the discovery of helium compounds by predicting what compounds might be stable under pressure, like a compound made of magnesium fluoride and a helium atom, or calcium fluoride and a helium atom.
Helium might be best known for inflating party balloons, but it's also used to cool superconducting magnets in cutting-edge scientific applications. The lightness and extensive use of helium have led to a dwindling supply of the element. The new study could not only offer new insights into the chemical function of helium, but also offer evidence to where more of it can be discovered.
Our work reveals that helium has the propensity to react with a broad range of ionic compounds at even low pressures, which implies that there might be much more of it in the Earth than we realize. Since most of the Earth’s minerals contain unequal numbers of positively and negatively charged ions, our work suggests that large quantities of helium might be stored in the Earth’s mantle.
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