1.

What is the order of bond enthalpies of halogens? Why is it not opposite to that of bond lengths?

Answer»

Solution :Bond lengths ofhalogens are in the ORDER :
`F_(2)ltCl_(2)ltBr_(2)ltI_(2)`.
Bond energies are expected in the order :
`F_(2)ltCl_(2)ltBr_(2)ltCl_(2)`.
But the experimental bond enthalpies are :
`Cl_(2)gtBr_(2)gtF_(2)gtI_(2)`.
Bond enthalpy of `F_(2)` is very less , because lone pair lone pair repulsions are APPRECIABLE in `F_(2)` as the bond LENGTH is small in `F_(2)`.
It was also thought , though not APPROPRIATE , that F-F bond is weak as multiple bond is not possible with no d-orbitals in the valence shell of fluorine .


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