Matter is anything that has mass and takes up space. Everything around us - books, balls, boxes - is made of matter. All matter consists of tiny particles called atoms and molecules that are constantly moving. The way these particles behave and arrange themselves determines what state the matter is in.
Solids are the first state of matter. In solids, particles are tightly packed in a regular, ordered arrangement. They vibrate in fixed positions but cannot move freely. This gives solids their definite shape and definite volume. The particles are held together by strong intermolecular forces. Examples include ice, wood, and metal. Solids resist compression and maintain their shape when moved from one container to another.
Liquids are the second state of matter. In liquids, particles are less ordered than in solids but remain close together. They can slide past each other while maintaining attraction. Liquids have definite volume but indefinite shape - they take the shape of their container. Particles have more kinetic energy than in solids. Examples include water, oil, and mercury. Liquids flow and conform to container shape while maintaining constant volume.
Gases are the third state of matter. Gas particles have high kinetic energy and are widely spaced, moving rapidly in all directions. Gases have indefinite shape and indefinite volume - they fill their entire container. Particles have weak intermolecular forces and gases are highly compressible. Examples include air, helium, and water vapor. Comparing all three states: solids have fixed arrangements, liquids flow but maintain volume, and gases expand to fill available space.
Matter can change from one state to another through phase transitions. There are six main transitions: melting changes solid to liquid, freezing does the reverse. Vaporization turns liquid to gas, while condensation reverses this. Sublimation goes directly from solid to gas, and deposition from gas to solid. These changes occur when energy is added or removed, affecting how particles move and arrange themselves.