Final answer:
During melting, the cohesive force between molecules is reduced, allowing the solid to transition to a liquid state. The melting point correlates with the strength of these attractive forces; weaker forces result in lower melting points and vice versa.
Step-by-step explanation:
During melting, the cohesive force or the force of attraction between identical molecules is weakened. This is because melting involves the absorption of energy (enthalpy of fusion), causing the molecules to vibrate with increased kinetic energy. As a result, the ordered structure of a crystalline solid breaks down, and the attractive forces holding molecules tightly together in the solid phase are overcome, allowing them to move freely in the liquid phase.
Condensation, on the other hand, is the change from a gaseous state to a liquid. When a gas cools, its particles have less kinetic energy and move closer together, permitting the attractive forces to become significant again, resulting in a phase transition to a liquid or solid, depending on the temperature.
The melting point of a substance depends on the strength of these attractive forces. Molecules with weak attractive forces form crystals with low melting points, whereas molecules with stronger forces have higher melting points.