Oxyacid

An oxoacid is an acid that contains oxygen. Specifically, it is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bound to oxygen that can dissociate to produce the H⁺ cation and the anion of the acid.

Generally, oxoacids are simply polyatomic anions attached to a positively-polarized hydrogen, which can be split off as a cation.

Under Lavoisier's original theory, all acids contained oxygen, which was named from the Greek ὀξύς (oxys: acid, sharp) and the root -γενής (-genes: creator). It was later discovered that some acids, notably hydrochloric acid, did not contain oxygen and so acids were divided into oxoacids and these new hydroacids.

All oxoacids have the acidic hydrogen bound to an oxygen atom, so bond strength (length) is not a factor, as it is with binary nonmetal hydrides. Rather, the electronegativity of the central atom (X) and the number of O atoms determine oxoacid acidity. With the same central atom X, acid strength increases as the number of oxygens attached to X increases. With the same number of oxygens around E, acid strength increases with the electronegativity of X.

Imidic acids are created by replacing =O with =NR in an oxoacid.

An oxoacid molecule contains the structure X−O−H, where other atoms or atom groups can be connected to the central atom X. In a solution, such a molecule can be dissociated into ions in two distinct ways:

If the central atom X is strongly electronegative, then it strongly attracts the electrons of the oxygen atom. In that case, the bond between the oxygen and hydrogen atom is weak, and the compound ionizes easily in the way of the former of the two chemical equations above. In this case, the compound XOH is an acid, because it releases a proton, that is, a hydrogen ion. For example, nitrogen, sulfur and chlorine are strongly electronegative elements, and therefore nitric acid, sulfuric acid, and perchloric acid, are strong acids.

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