Oxides of halogen

Fluorine reacts readily and directly with oxygen (unlike the other halogens) to give oxygen fluorides rather than true "oxides" in the conventional sense, since in these compounds fluorine, being more electronegative than oxygen, is assigned the -1 oxidation state and oxygen is formally in a positive oxidation state (the reverse of the usual convention) — the two best-characterised examples are oxygen difluoride, OF2, and dioxygen difluoride, O2F2 (with O4F2 also known). The other, less electronegative halogens do not react directly with oxygen under ordinary conditions, but a range of true halogen oxides — in which the halogen itself is oxidised by oxygen and so shows a positive oxidation state — can be prepared by indirect methods. Chlorine forms the widest range: dichlorine monoxide Cl2O (+1), chlorine dioxide ClO2 (+4, an odd-electron radical widely used as a bleaching and water-disinfection agent), dichlorine hexoxide Cl2O6 (+6) and dichlorine heptoxide Cl2O7 (+7), along with the mixed-oxidation-state Cl2O4 (chlorine perchlorate, formally +4 average). Bromine forms only the lower oxides, Br2O (+1) and BrO2 (+4), reflecting its intermediate reactivity between chlorine and iodine. Iodine, being the lea …