Question

Select the correct order with respect to lattice energy of alkali metals fluorides:

• A. $RbF<KF<NaF<LiF<CsF$
• B. $KF<NaF<LiF<CsF<RbF$
• C. $NaF<LiF<CsF<RbF<KF$
• D. $CsF<RbF<KF<NaF<LiF$

Answer 1

The correct option is D $CsF<RbF<KF<NaF<LiF$

In the given alkali metal halides, the anion is the same ($F^{-}$ ion). Lattice energy depends on the size of the cation. It is inversely proportional to the size of the cation.

Thus, as the size of the cation increases, the lattice energy decreases. Therefore, the smallest size is of $L{i}^{+}$ and hence, $LiF$ will have the highest lattice energy.

Hence, the correct order is $CsF<RbF<KF<NaF<LiF$.