Hydroxide, hy DROK syd, is a chemical ion. An ion is one or a group of atoms with an electric charge that act together in chemical reactions. The hydroxide ion has a negative charge and is composed of a hydrogen atom and an oxygen atom. Many compounds containing the hydroxide ion dissolve in water solutions, producing ionic solutions. For example, sodium hydroxide dissolves to form sodium ions and hydroxide ions in water. The hydroxide ion combines with metals and certain nonmetals to form compounds that are basic, acidic, amphoteric (basic or acidic), or neutral.