Particles are held together by forces of attraction between molecules e.g., covalent, van der waals and hydrogen bonds. Such type of forces are easily denatured by slight increase in temperature. The solid nature of the compound melts to liquid form. The size of the molecule determines the amount of intermolecular forces available. Smaller molecules have fewer intermolecular forces compared to larger ones thus the melting point is low. Larger molecules have more intermolecular forces that require more energy to break.
