The intermolecular forces of attraction are the bonds that the particles in the matter form with each other. The stronger the bond, the stronger are the intermolecular forces of attraction between them. When the intermolecular forces of attraction are strong, a higher amount of heat energy will be needed to breaks these bonds and hence the melting point of strong intermolecular forces of attraction will be higher.
The latent heat of vaporization is higher than latent heat of fusion because the intermolecular space between gas particles is the greatest and the intermolecular forces of attraction are almost negligible. Hence more energy is needed to convert liquid into a gas. The transition of solid into liquid requires less energy because the energy used for this is only needed to decrease the intermolecular attraction between the particles.
