Change in Physical State. Heat also affects how molecules interact with each other. Heating a solid above a certain temperature will cause it to melt to form a liquid; further heating causes this liquid to boil to form a vapor.
When water is in its solid state (ice) , the water molecules are packed close together preventing it from changing shape. Ice has a very regular pattern with the molecules rigidly apart from one another connected by the hydrogen bonds that form a crystalline lattice.
Change of state. Substances can change state, usually when they are heated or cooled. For example, liquid water turns into steam when it is heated enough, and it turns into ice when it is cooled enough. The closeness, arrangement and motion of the particles in a substance change when it changes state.