1) Take a small amount of sodium chloride (NaCl) on a metal spatula (having an insulated handle).
2) Heat it directly over the flame of a burner.
3) We will see that sodium chloride (NaCl) does not melt easily.
4) Sodium chloride melts (and becomes a liquid) only on strong heating.
5) This shows that sodium chloride which is an ionic compound possess strong bonds.
6) So it has a high melting point.
7) Whereas covalent compound like naphthalene and carbon tetra chloride has low boiling points such as 80°C and 77°C respectively.
8) The force of attraction between the molecules of a covalent compound is very weak.
9) Only a small amount of heat energy is required to break these weak molecular forces, due to which covalent compounds have low melting points and low boiling points.