Question

The melting point of NaBr is $682{}^{\circ }C$ while that of NaF is $988{}^{\circ }C$. The principle reason behind the melting point of NaF being higher than that of NaBr is:

• A. The two crystal are not isomorphous
• B. The molar mass of $NaF$ is lower than that of $NaBr$
• C. The internuclear distance $(r_c+r_a)$ of $NaBr$ is greater than $NaF$
• D. The bond in $NaBr$ has a higher covalent character than the bond in $NaF$

Answer 1

The correct option is D The bond in $NaBr$ has a higher covalent character than the bond in $NaF$

According to Fajan's Rule, it can be concluded that $NaF$ is more ionic in nature. This means that the lattice energy of $NaF$ is very high, thereby giving it an exceptionally high melting point.