3. Forms of matter

Solids, liquids, and gases are the great states of matter; a solid has a shape and a volume, a liquid has a volume but no shape, and a gas has neither shape nor volume. ‘Forms of matter’ explains how these different states arise from a competition between opposites: thermal motion driving particles apart and the attractive forces between atoms pulling them together, repulsion and attraction. The ‘glue’ that holds electrons to atoms, brings atoms together to form molecules, and draws molecules together to make solids and liquids, is electricity. Chemical bonds, crystals, intermediate states, and plasma—the fourth state of matter—are discussed.