Heteronuclear molecule in the context of "Homonuclear"

Diatomic molecules (from Greek di- 'two') are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen (H₂) or oxygen (O₂), then it is said to be homonuclear. Otherwise, if a diatomic molecule consists of two different atoms, such as carbon monoxide (CO) or nitric oxide (NO), the molecule is said to be heteronuclear. The bond in a homonuclear diatomic molecule is non-polar.

The only chemical elements that form stable homonuclear diatomic molecules at standard temperature and pressure (STP) (or at typical laboratory conditions of 1 bar and 25 °C) are the gases hydrogen (H₂), nitrogen (N₂), oxygen (O₂), fluorine (F₂), and chlorine (Cl₂), and the liquid bromine (Br₂).

The helium hydride ion, hydridohelium(1+) ion, or helonium is a cation (positively charged ion) with chemical formula HeH. It consists of a helium atom bonded to a hydrogen atom, with one electron removed. It can also be viewed as protonated helium. It is the lightest heteronuclear ion, and is believed to be the first compound formed in the Universe after the Big Bang.

The ion was first produced in a laboratory in 1925. It is stable in isolation, but extremely reactive, and cannot be prepared in bulk, because it would react with any other molecule with which it came into contact. Noted as the strongest known acid—stronger than even fluoroantimonic acid—its occurrence in the interstellar medium had been conjectured since the 1970s, and it was finally detected in April 2019 using the airborne SOFIA telescope.