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.
Solids, liquids and gases can all transform from one into the other. This happens every day all over our globe with the water cycle. For example: when water evaporates from the sea and turns into clouds or when it condenses from cloud into rain, when a lake freezes and turns into ice, or when ice melts and turns back into water. When matter changes states it is to do with the amount of energy that the particles have.