KS2 SATs Science: States of Matter Guide

Solids, liquids and gases

Solids have a fixed shape and volume. Liquids have a fixed volume but take the shape of their container. Gases have no fixed shape or volume and spread out to fill the space available.

Changing state

Melting turns a solid into a liquid; freezing turns a liquid into a solid. Evaporation turns a liquid into a gas; condensation turns a gas back into a liquid. These changes happen at specific temperatures for a given substance.

The water cycle

Water evaporates from seas and lakes, rises and cools to condense into clouds, then falls as precipitation (rain, snow, hail). This water collects and flows back to the sea, and the cycle repeats.

Common mistakes

• Mixing up melting and dissolving — dissolving is a substance mixing into a liquid, not changing state.
• Thinking evaporation only happens when water boils — it can happen at any temperature, just more slowly.
• Forgetting that condensation is a gas turning into a liquid, not the other way round.