States of matter — Chemistry, 7–10 years
The same material can be a solid, liquid or gas. Its state helps explain why ice keeps its shape, water flows and steam spreads.
What a state tells us
A solid keeps its own shape, a liquid takes the shape of its container, and a gas spreads to fill the space around it. Heating or cooling can change one state into another without changing what the material is. Ice, water and water vapour are all made of water.
Why notice the state?
People needed to predict how materials would behave when stored, heated or poured. Knowing the state helps with simple problems: choosing a bottle for juice, leaving room for ice to melt, or keeping a gas in a sealed container. It is a way to describe useful behaviour, not just a label.
Ice on a warm table
1. Put one ice cube on a plate. It keeps its shape, so it is a solid. 2. Leave it in a warm room; heat makes it melt. 3. The melted water flows and takes the plate’s shape, so it is a liquid. 4. If the water is heated enough, some becomes invisible water vapour, a gas.
The shape trap
A common thought is that anything with no fixed shape must be a gas. That seems reasonable because both liquids and gases can spread out. The useful test is what happens in a container: a liquid keeps one amount and forms a pool, while a gas expands to fill all the available space.
States around us
A freezer uses a change of state to turn liquid water into ice, and a kettle turns liquid water into steam. Weather also depends on states: water vapour can cool into tiny liquid drops in a cloud. These examples are useful because the material stays water while its behaviour changes.
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