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.

Solution:

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’.