Question

Which compound possesses the greatest lattice energy?

• A. $LiBr$
• B. $LiCl$
• C. $LiI$
• D. $LiF$

Answer 1

The correct option is D $LiF$

Lattice energy is proportional to the product of the charges on the ions and inversely proportional to the separation between the centres of the ions, that is the size of the ions.
$LiBr\to L{i}^{+}+B{r}^{-}$
$LiCl\to L{i}^{+}+C{l}^{-}$
$LiI\to L{i}^{+}+I^{-}$
$LiF\to L{i}^{+}+F^{-}$
Since in all the cases $L{i}^{+}$ is the cation, the deciding factor here will be the size of the anions.
Size of anions $(F^{-}<C{l}^{-}<B{r}^{-}<I^{-})$ increases down the group.
Therefore, $LiF$ has the greatest lattice energy.