States of Matter

Solid, liquid, and gas — how heating and cooling change matter

Matter exists in three main states: solid, liquid, and gas. In a solid, particles are packed tightly and vibrate in place — the substance has a definite shape and volume. In a liquid, particles can flow past each other — the substance has definite volume but takes the shape of its container. In a gas, particles move freely and fast — the substance has no definite shape or volume. Heating gives particles more energy; cooling takes it away. The temperature at which a solid becomes liquid is the melting point; the temperature at which liquid becomes gas is the boiling point. Different materials have different melting/boiling points.