Halogen oxides

The entire halogen family forms oxides. Many halogen oxides have been reported however most of them are unstable. These are illustrated in the table shown below.

Halogen–oxygen bonds are highly covalent due to the similarities in electronegativity of halogens and oxygen. Fluorine is more electronegative than oxygen; therefore compounds of fluorine with oxygen are taken as fluorides of oxygen instead of oxides of fluorine.

I₂O₅ is the only halogen oxide that is stable with respect to the dissociation into elements. Chlorine oxides decompose violently whereas the bromine oxides are the least stable among the halogen oxides. Of these just Cl₂O and ClO₂ find some practical significance as bleaching agents in paper pulp and flour industries; I₂O₅ is employed in the estimation of CO.

Oxidation State	Fluorine	Chlorine	Bromine	Iodine
+ 1	OF₂	Cl₂O	Br₂O	–
+ 2	F₂O₂			–
+ 3	–	Cl₂O₃
+ 4	–	ClO₂	BrO₂	I₂O₄
+ 5	–	–	–	I₂O₅
+ 6	–	Cl₂O₆	–	–
+ 7	–	Cl₂O₇	–	–

Only the structures of OF₂, Cl₂O, Br₂O, Cl₂O₇ and I₂O₅ are definitely known. Structures of the monoxides can be illustrated on the basis of VSEPR theory. These oxides have tetrahedral structure having two lone pairs on oxygen. Therefore, the molecule is 'V' shaped or angular in shape.

The bond angles FOF < ClOCl < BrOBr.

This is due to electrons in case of OF₂ are closer to fluorine because of high electronegativity of F as compared to Cl or Br. The bonded electron pairs in Cl₂O and Br₂O are closer to oxygen making the repulsion between them more and thus reducing the lone pair-lone pair repulsion on oxygen to certain extent.

As well due to the bulkiness of Cl and Br, the angles ClOC1 and BrOBr increase to such an extent that they are greater than 109^°28', the tetrahedral angle. The figure shown below exhibits some of the structures of chlorine oxides.

Cl₂O: When heated or subject to a spark, Cl₂O explodes to Cl₂and O₂. Dichlorine monoxide reacts with water to form an orange-yellow solution of hypochlorous acid.

Cl₂O + H₂O → 2HOCl

ClO₂: Chlorine dioxide is a yellowish gas at room temperature .The structure of ClO₂ is equivalent to SO₂ with one extra electron, resulting in a paramagnetic unpaired electron species.

Unusually, despite the unpaired electron configuration, ClO₂ shows no tendency to dimerize, unlike the analogous NO₂ molecule.

Cl₂O₇: Dichlorine heptoxide is a relatively stable oil. Dehydration of perchloric acid with P₄O₁₀ produces Cl₂O₇.Hence the heptoxide is the anhydride of perchloric acid.