Question

"The melting point of $LiCl$ is higher than $NaCl$."
Answer whether the above statement is true or false.
If true enter 1, else enter 0.

Answer 1

Comparison of melting points of ionic compounds is generally done by considering the following two factors:

1. Charge of the cation/anion : More the charge of cation or anion, stronger will be the forces of attraction between the ions and higher will be the melting point. In this case, the charge is same as they belong to the same group.

2. Ionic radii:More the distance between ions, lesser will be the strength of the bond giving rise to lesser melting point.

Going by the above rules, the order should have been:
LiCl>NaCl>KCl>RbCl
(Since charges of the ions are same for each molecule and cationic radius increases down the group.)
BUT, LiCl, owing to its small size, due to excessive polarization (Fajans' rules), exhibits high covalent character in contrast to other group members which are ionic and is placed last in the order. Hence, the new order would be:
NaCl>KCl>RbCl>LiCl
The other ions, being similar in size to chloride ions, do not undergo much polarization.

Hence, the correct answer is 0.