The compounds of one halogen with the other are called inter halogens or inter halogen compounds. The main reason for their formation is the large electronegativity and the size differences between the different halogens. Taking A as the less electronegative and B as the more electronegative halogen, they are divided into the following four types the less electronegative halogen (A) is always written first.

These interhalogen compounds are unstable and more reactive

(i) General properties

(a) Largest halogen always serves the central atom.

(b) The highest interhalogen compound i.e. IF₇ is obtained with iodine, the largest halogen attached to the smallest one

(c) The bonds in interhalogen compounds are essentially covalent.

(d) Thermal stability decreases as the size difference decreases and increases as the polarity of the bond increases. Thus ClF is thermally more stable as compared to IBr.

(e) They ionize in solution or in the liquid state,

2lCl I⁺ + ICl^–₂; 2lCl₃ ICl₂⁺ + ICl^–₄

(f) Hydrolysis of interhalogen compounds always produces a halide ion derived from smaller halogen and oxyhalide derived from larger halogen, ;

ICI + H₂O —> Cl^– + OI^– + 2H⁺ ; BrF₅3H₂O —> 5F^– + BrO₃^– + 6H^–

(g) They are strong oxidizing agents.

(h) Largest number of interhalogens are formed by fluorine due to its smaller size and higher electronegativity or oxidizing power.

(ii) Structure: Interhalogen compounds are,

(a) AB type i.e. ICl, IBr, IF etc, are linear

(b) AB₃ type i.e. IF₃, ClF₃, BrF₃ have distorted trigonal bipyramidal (dsp³-hybridization) structures of T-shape due to two lone pairs in equatorial positions ICl₃ is dimeric, I₂Cl₆ and has a planar structure.

(c) AB₅ types i.e. BrF₅, IF₅ have distorted octahedral (d²sp³-hybridization) shapes or square pyramidal due to a lone pair one of the axial positions.

(d) AB₇ type i.e. IF₇, have pentagonal bipyramidal (d³sp³-hybridization) structures.