Particles and their behaviour · MODEL

The particle model

What is everything made of?

Draft — not yet science-reviewed.

Start here

Half a glass of water, half a glass of alcohol

Pour 50 cm³ of water into 50 cm³ of alcohol. You now have 100 cm³ of liquid. Except you don't — you have about 97 cm³.

Where did the missing 3 cm³ go?

Your turn

Before anyone explains it — commit to an answer. Where did the missing 3 cm³ go?

Here is the answer. Everything is made of tiny particles with gaps between them. Water particles and alcohol particles are not the same size. Pour them together. The smaller particles drop into the gaps between the bigger ones. So the mixture packs tighter. Nothing is lost. Nothing is destroyed. Every particle you poured in is still there. The total just takes up less room than the two volumes added together.

Two measuring cylinders, before and after mixing.

Your turn

So matter comes in pieces with gaps between them. How small do the pieces go? Imagine cutting a lump of copper in half, then in half again, over and over.

Your turn

The model needs gaps. So what is actually inside a gap between two particles of a gas?

Think again

Here is the idea to kill, in the words students really write: 'the gaps between the particles are filled with air.' If that were true, what would be in the gaps between the air particles?

Particles drawn as circles in a solid, a liquid and a gas.

So here is the whole model, in three lines. All matter is made of particles. The particles are always moving. Between them is empty space — nothing at all. Every single thing in this unit is worked out from those three lines.

Words to know

particle
One of the tiny pieces that all matter is made from, far too small to see.

In this unit 'particle' means atoms or molecules. You will meet those names properly in C2.

matter
Anything that has mass and takes up space.
model
A simple picture or idea that helps explain something we cannot see directly.

A model does not have to be a perfect copy to be useful. L6 asks how far this one can be pushed.

Your turn

Three words this lesson runs on. Say the word out loud before you tap each card — no peeking first.

Your turn

Now build the model yourself instead of reading it. Draw ten particles of a gas in a box, and label what is between them.

Check your answer
  • Particles drawn as separate circles, not touching
  • The space between them labelled 'nothing' or 'empty'
  • Particles roughly evenly spread

Mastery ladder

① Recall

What is between the particles in a gas?

② Apply

50 cm³ of water is mixed with 50 cm³ of alcohol and the total is 97 cm³. What does this tell you about particles?

③ Explain

Explain why mixing two liquids can give a total volume smaller than the two volumes added together.

Mark your answer against this list
  • Says matter is made of particles
  • Says there are spaces between the particles
  • Says the smaller particles fit into those spaces
  • Says no particles are lost

④ Produce

A student says: 'If I squash a gas, I am squashing the particles smaller.' Write a reply that corrects them.

Mark your answer against this list
  • Says the particles themselves do not change size
  • Says the spaces between particles get smaller
  • Uses the word 'particle' correctly

Key note

All matter is made of tiny moving particles. Between them is empty space — not air. Squashing a substance closes the spaces; it never shrinks the particles.

Going further

Just how small is too small to see? One drop of water holds more particles than there are drops of water in all the oceans on Earth. So no microscope in any school will ever show you one.

Your turn

Use that number on someone else. Explain to a Year 5 student why we cannot see a single particle with a school microscope.

Check your answer
  • Says particles are far smaller than anything a light microscope can show
  • Does not say 'because they are invisible'

At GCSE this becomes

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