Matter and Its Three States

Put your water bottle in the freezer overnight and it turns hard. Pull it out and it melts back into water. Leave a puddle in the sun and it disappears as vapour into the air. The water has not changed into something new — it is still water, just in a different state. Everything around you — your school bag, the air you breathe, the juice in your cup — is made of tiny particles, and the state those particles are in depends on how much energy they have.

Parents: the sim below lets your child set a temperature and watch the particles rearrange. Let them predict what happens at each step before they click Heat or Cool — saying the keyword out loud ("the liquid will evaporate by boiling") is what makes it stick.

By the end you will be able to describe the three states of matter and name exactly what happens to the particles when matter heats up or cools down. The four ideas we will master are: solid, liquid, gas, and the state changes between them.

Solid — fixed shape, fixed volume

Think about your wooden ruler. You can hold it upside down, put it on your desk, or drop it in your bag — and it keeps exactly the same shape every time. That is what makes something a solid. The particles in a solid are packed tightly together in a regular pattern, like eggs in a tray. They do not flow; they only vibrate in place. Because the particles cannot move freely, a solid has a fixed shape and a fixed volume (it takes up the same amount of space no matter which container you put it in).

Ice, rock, glass, your pencil, the HDB wall — these are all solids.

Liquid — fixed volume, no fixed shape

Pour water into a cup, then pour it into a bowl. The shape changes to match the container, but the amount of water stays the same. That is a liquid. Liquid particles are still close to each other, but they can slide and flow past one another freely. This means a liquid has a fixed volume (same amount) but no fixed shape (takes the shape of its container).

Water, juice, cooking oil, and even liquid mercury are all liquids.

Gas — no fixed shape, no fixed volume

Open a bottle of your mother's perfume in one corner of the room and within seconds you can smell it everywhere. That is a gas. Gas particles have so much energy that they spread out and fill any space available. A gas has no fixed shape and no fixed volume — it expands to fill whatever container it is in. The air around you, steam rising from a pot of boiling water, and the carbon dioxide in a fizzy drink are all gases.

How heating and cooling change the state

Matter moves from one state to another when energy is added (heating) or taken away (cooling). Each change of state has a specific name your marker expects.

Try the particle experiment. Predict what happens to the particles when you heat the solid, then check.

🔬

Heat it up or cool it down — watch the particles!

🤔 Predict first: When you heat ice, the particles…

Pack closer togetherSpread far apartParticles spread far apart and move freely

Here is the complete map of state changes:

Watch out — these are easily mixed up

Quick recap

🎯 Mastery check

Answer all 8 — your progress is saved on this device.

1. An ice cube has a fixed shape that does not change even when you hold it differently. Why?

   Its particles are far apart and move freelyIts particles are tightly packed and can only vibrate in placeIts particles can slide past one another

2. You pour orange juice from a round cup into a square cup. The shape of the juice changes but the amount stays the same. What state is orange juice?

   SolidLiquidGas

3. You spray air freshener in one corner of the classroom and soon everyone can smell it. Which property of a gas explains this?

   A gas has a fixed shapeA gas expands to fill all the available spaceA gas has a fixed volume

4. Ice is left on a warm void deck for an hour and turns into water. What is the name of this change of state?

   BoilingCondensationMelting

5. Water is heated in a pot until it bubbles strongly and steam rises. What is the name of this change of state?

   FreezingBoilingMelting

6. Cold water droplets form on the outside of a glass of iced water. What caused this?

   Water leaked through the glassWater vapour in the air condensed on the cold surfaceThe ice inside melted and flowed out

7. A student says "the juice dissolved when I put it in the freezer." What is wrong with this statement?

   The juice should have boiled, not frozenThe correct word is froze — juice changes from a liquid to a solid when cooled, which is freezing, not dissolvingNothing is wrong, dissolving and freezing mean the same thing

8. Which of the following correctly describes a gas?

   Fixed shape and fixed volumeNo fixed shape but fixed volumeNo fixed shape and no fixed volume

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