When a solid melts it does not change directly into a gas. This process of changing a solid into a gas without passing through the liquid state is called sublimation.

When a solid melts, it undergoes a phase transition from a solid state to a liquid state. The particles of the solid become less tightly packed and they can move more freely.

If the temperature of the liquid is raised further, the particles will become even more energetic and they will eventually reach a point where they can break free of the liquid's surface tension. This is the point at which the liquid boils and turns into a gas.