Hydroxide vs. Hydroxyl

Hydroxide

Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. A hydroxide attached to a strongly electropositive center may itself ionize, liberating a hydrogen cation (H+), making the parent compound an acid.

The corresponding electrically neutral compound HO• is the hydroxyl radical. The corresponding covalently-bound group –OH of atoms is the hydroxy group.

Hydroxide ion and hydroxy group are nucleophiles and can act as a catalysts in organic chemistry.

Many inorganic substances which bear the word “hydroxide” in their names are not ionic compounds of the hydroxide ion, but covalent compounds which contain hydroxy groups.