Chemistry Lab · Free lesson · 12 minutes
The particles do not melt
Explain a change of state using what we observe, what particles do and the symbols we write.
SS1 · particle model01 · Think first
Start with a question.
Ice becomes liquid water. Does each water molecule turn into a different substance—or does the way the molecules are arranged change?
What you already know
- Identify solid, liquid and gas
- Distinguish a substance from a single particle
- Recognise the formula H₂O
02 · See it
See it · three ways to explain
Same substance. Different arrangement.
- Observe · macroscopic
- Keeps its shape.
- Explain · particle model
- Particles are close together and vibrate about fixed positions.
- Represent · symbolic
- H₂O(s)
A qualitative model: particles are represented by circles, not literal blue balls. Size and count stay the same between views. Motion is described in words; these still diagrams do not imply that particles stop moving. No practical experiment is required.
03 · Show steps · explain why
One justified step at a time.
- 1
Observe: a solid keeps its shape; a liquid can flow.
Start with the bulk behaviour we can see. This is the macroscopic description.
04 · Mistake clinic
Find the first wrong idea.
Heating makes each water molecule bigger, so it becomes liquid.
Compare the correction and its reason
Heating changes particle energy and arrangement; the molecules remain water molecules.
The model must distinguish the particle from the spaces and motion between particles. A state change preserves chemical identity.
Check: Compare the three diagrams: the count and drawn size are unchanged. The diagrams are qualitative models, not scale drawings.
A mistake is evidence about the next idea to repair. It is not a label for the learner.
05 · Your turn
Try first. Then use a hint.
06 · Check & reflect → next step
Understanding includes explaining.
Can you connect an observation, a particle explanation and a state symbol without saying that a particle itself melts?
Next, distinguish a physical change from a chemical reaction. Ask a tutor for help if substance and particle still mean the same thing to you.
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JEM-CH-C01-001 · Phase 5A · Chemistry foundations · Lab 03 · Matter, Particle Model, States & Diffusion, printed pp. 20–21
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