The melting point of KCl is 776 C whereas the melting point of NaCl is 801 C.

Question

1. Identify the type of bonding in each substance.

A: Both NaCl and KCl are ionic.

2. Account for the differences in the boiling points of the substances using principles of atomic structure, bonding, and/or intermolecular forces.

Answer 1

K+ is a larger ion than Na+. Therefore the K+ and Cl- ions can't get as close as the do with Na+ and Cl-. That results in a lower bond energy for KCl,
So a lower KCl boilng point results because less thermal energy is needed to break the bond.