1.

Arrange the following in the order of property indicated for set : F_2,Cl_2 , Br_2, I_2 - increasing bond dissociation enthalpy .

Answer»

Solution :Bond DISSOCIATION enthalpy is expected to decrease as the bond distance between the atoms increases from `F_2` to `I_2` due to the corresponding increase in the size of the ATOM. However, we observe that the F - F bond dissociation enthalpy is smaller than that of Cl - Cl and EVEN smaller than that of Br - Br. This is due to the reason that the F atom is very small, the THREE lone pairs of electrons on each F atom repel the bond pair holding the F-atoms in `F_2` molecule. Thus, the bond dissociation enthalpy increases in the order :
`I_2 lt F_2 lt Br_2 lt Cl_2`


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