Helium hydride ion

The helium hydride ion, also called helonium, is a cation (chemical compound with a positive electric charge) made of helium and hydrogen. It has the chemical formula . It first formed shortly after the Big Bang, making it the oldest molecule in the universe.

Helium hydride is the strongest known acid. It cannot be made as a liquid or solid because it will react with any other molecule it touches.

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Category:Helium compounds
Category:Superacids
Category:Binary acids
Category:Onium ions