Oxoacids of halogens

Chlorine is the only halogen to form the complete series of four types of oxoacid — hypochlorous acid (HOCl), chlorous acid (HClO2), chloric acid (HClO3) and perchloric acid (HClO4) — spanning oxidation states +1, +3, +5 and +7 respectively. Bromine and iodine form the analogous hypohalous, halic and perhalic acids (HOBr/HBrO3/HBrO4 and HOI/HIO3/HIO4) but do not form a stable halous acid (HBrO2 and HIO2 are not isolable). Fluorine, uniquely, forms only the +1 acid, hypofluorous acid (HOF), since its extreme electronegativity and small size prevent it from ever being oxidised to a positive state higher than +1, or indeed from being the central atom of a larger oxo-anion framework at all. Across this whole family, for a given halogen, the oxidising power of the oxoacids decreases steadily with increasing oxidation state/number of oxygens, in the order HOX > HXO2 > HXO3 > HXO4 — the lower oxidation states are less thermodynamically stabilised by the additional oxygens and so are more reactive oxidisers, whereas the higher oxoacids (like HClO4) are comparatively more stable, weaker oxidants but stronger Brønsted acids, since the acid strength within …