Chlorine oxoanions are negatively charged polyatomic ions consisting of chlorine and oxygen. The chlorine atom is in an odd-number positive oxidation state, and the atom is surrounded by oxygen atoms and lone pairs of electrons. They are all oxidizing, but their stability varies, and some may have reducing tendencies. The four types of chlorine oxoanions are hypochlorites, chlorites, chlorates, and perchlorates.
The oxoanions of chlorine are all quite unusual in their properties. As the oxygen content of the anion increases, the oxidizing ability of the ion actually decreases, as they become kinetically poorer oxidizers. More oxygenated anions are more stable with respect to oxidation and reduction. With light heating, hypochlorites will disproportionate into chlorates and chlorides, and chlorates will disproprtionate into perchlorates and chlorides. Perchlorates will convert to chlorides, with the loss of oxygen, in the presence of intense heat.
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Chlorine oxoanion salts can be prepared by electrolysis of an alkali metal chloride and specific voltages.