In chemistry, a hydride is formally the anion of hydrogen, H−. The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms, are called hydrides: water is a hydride of oxygen, ammonia is a hydride of nitrogen, etc. For inorganic chemists, hydrides refer to compounds and ions in which hydrogen is covalently attached to a less electronegative element. In such cases, the H centre has nucleophilic character, which contrasts with the protic character of acids. The hydride anion is very rarely observed.