Chemistry Interhalogen Compounds

Topics Covered :

● Preparation of Interhalogen Compounds
● Properties of Interhalogen Compounds
● Uses of Interhalogen Compounds

Interhalogen Compounds :

`=>` When two different halogens react with each other, interhalogen compounds are formed.

`=>` They can be assigned general compositions as `color{red}(XX′ , XX_3 ′, XX_5 ′)` and `color{red}(XX_7 ′)` where `color{red}(X)` is halogen of larger size and `color{red}(X′)` of smaller size and `color{red}(X)` is more electropositive than `color{red}(X′)`.

`=>` As the ratio between radii of `color{red}(X)` and `color{red}(X′)` increases, the number of atoms per molecule also increases.

`=>` Therefore, iodine (VII) fluoride should have maximum number of atoms as the ratio of radii between `color{red}(I)` and `color{red}(F)` should be maximum. That is why its formula is `color{red}(IF_7)` (having maximum number of atoms).

Preparation :

`=>` The interhalogen compounds can be prepared by the direct combination or by the action of halogen on lower interhalogen compounds. The product formed depends upon some specific conditions.

`=>` `color{red}("Example")` :

`color{red}(undersettext{(equal volume)}(Cl_2) +F_2 overset(437K)→ 2ClF \ \ \ \ \ \ I_2 + undersettext{(excess)}(3Cl_2) → 2ICl_3)`

`color{red}(Cl_2 + undersettext{(excess)} (3F_2) overset(573 K)→ 2ClF_3 ; \ \ \ \ \ \ \ \ undersettext{(dilutedwith water)}(Br_2) +3F_2 → 3BrF_3)`

`color{red}(undersettext{(equimolar)}(I_2) +Cl_2 → 2I Cl ; Br_2 + undersettext{(excess)}(5F_2) → 2BrF_5)`

Properties :

`=>` Some properties of interhalogen compounds are given in Table 7.11.

`=>` These are all covalent molecules and are diamagnetic in nature.

`=>` They are volatile solids or liquids except `color{red}(ClF)` which is a gas at `298 K`.

`=>` Their physical properties are intermediate between those of constituent halogens except that their m.p. and b.p. are a little higher than expected.

`=>` Their chemical reactions can be compared with the individual halogens.

`=>` In general, interhalogen compounds are more reactive than halogens (except fluorine).

● This is because `color{red}(X–X′)` bond in interhalogens is weaker than `color{red}(X–X')` bond in halogens except `color{red}(F–F)` bond.

● All these undergo hydrolysis giving halide ion derived from the smaller halogen and a hypohalite (when `color{red}(XX′)`), halite (when `color{red}(XX′_3)`), halate (when `color{red}(XX′_5)`) and perhalate (when `color{red}(XX′_7)`) anion derived from the larger halogen.

`color{red}(XX' + H O → HX' + HOX)`

`=>` Their molecular structures are very interesting which can be explained on the basis of VSEPR theory (Example 7.19).

`=>` The `color{red}(XX'_3)` compounds have the bent `‘T’` shape, `color{red}(XX'_5)` compounds square pyramidal and `color{red}(IF_7)` has pentagonal bipyramidal structures (Table 7.11).

Uses :

`=>` These compounds can be used as non aqueous solvents.

`=>` Interhalogen compounds are very useful fluorinating agents.

`=>` `color{red}(ClF_3)` and `color{red}(BrF_3)` are used for the production of `color{red}(UF_6)` in the enrichment of `color{red}(text()^(235)U)`.

`color{red}(U(s) +3ClF_3 (l) → UF_6 (g) +3Cl F (g))`

Q 3010791619

Deduce the molecular shape of `BrF_3` on the basis of VSEPR theory.


The central atom Br has seven electrons in the valence shell. Three of these will form electronpair bonds with three fluorine atoms leaving behind four electrons. Thus, there are three bond pairs and two lone pairs. According to VSEPR theory, these will occupy the corners of a trigonal bipyramid. The two lone pairs will occupy the equatorial positions to minimise lone pair-lone pair and the bond pairlone pair repulsions which are greater than the bond pair-bond pair repulsions. In addition, the axial fluorine atoms will be bent towards the equatorial fluorine in order to minimise the lone-pair-lone pair repulsions. The shape would be that of a slightly bent ‘T’.