Chemists at the Polish Academy of Sciences have discovered that the element krypton may not be quite as unreactive as previously thought, and that while it might not be able to form Superman-slaying kryptonite crystals – for which it would need to bond with nitrogen – it can bond with oxygen, forming krypton monoxide.
As a noble gas, krypton’s atoms have a full outer shell of electrons, and therefore display an extreme reluctance to undergo chemical reactions and bond with other substances to form molecules. Therefore, like other noble gases such as helium and argon, krypton was for a long time thought to be inert.
However, in 2003, scientists reported that under certain extreme conditions, krypton could be coaxed into reacting with hydrogen and carbon atoms in order to form compounds. Building on this, a new study in the journal Scientific Reports provides evidence that krypton can also bond with oxygen to form krypton oxides, but only under intense pressure.
Though the study authors did not actually observe this chemical reaction in practice, they did use genetic algorithms in order to determine the theoretical likelihood of krypton-oxygen molecules forming. Such algorithms enable scientists to simulate the chemical interactions between atoms and molecules under pre-defined hypothetical conditions, and have previously been used to reliably predict the viability of many chemical reactions.
According to the team’s calculations, krypton and oxygen atoms can be brought close enough together to form a covalent bond – whereby an electron is shared between the two atoms – at a pressure of 285 gigapascals. The stability of the compounds generated by this reaction is dependent upon several factors, such as the number of bonds formed and the spatial arrangement of atoms in relation to one another.
For instance, according to the algorithms used by the researchers, these compounds can only survive if the ratio between krypton and oxygen atoms is 1:1, producing krypton monoxide. Moreover, stability can only be maintained if atoms are connected to each other in zig-zag chains, with no intermolecular bonds between these chains.
When this occurs, the substance – which should exist as a dark crystal – can remain intact even when the pressure is raised to 500 gigapascals. However, since such extreme pressures only occur deep within the core of some planets, where neither oxygen nor krypton are found, it seems impossible that krypton monoxide could actually exist in nature.