The particle model treats matter as tiny particles that move and attract each other. It explains states, diffusion, compressing gases and expansion very well. It can't explain colour, why substances react, or electricity, because it treats particles as plain balls with no parts. Scientists keep a model for what it does well and use other models for the rest.
A street map is perfect for finding a café and useless for knowing how steep the hill is. Scientific models are like that too.
A short lesson: what the particle model is good at, and where it stops.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Practise: A few on your own, to check you have it.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: is the model wrong?
ExploreTry it on the board and compare what happens with your prediction.
Explore: a prediction that works
Try it yourselfNothing is saved: start again as often as you like.
Lift the barrier for a gas and for a liquid. Which mixes faster?
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: scope and limits
In your book: write one thing the particle model explains well and one thing it can't. For each, give the reason, starting "Because the model says particles…".
Can the particle model explain it?
A smell spreading across a room
Air being easy to squash but water not
A metal bar getting longer when heated
Why copper is orange and gold is yellowPlain balls have no colour of their own.
Why iron rusts but gold doesn'tReactions need atoms with parts that join and swap.
Why metals conduct electricity
PractiseA few on your own, to check you have it.
Mix it up
Elaborate TypicalUse the same idea in a new context.
Elaborate: a better model
Elaborate WiderUse the same idea in a new context.
Elaborate: how the idea grew
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
The particle model says matter is made of tiny particles that move and attract each other.
It explains states, diffusion, compressing gases and expansion very well, and evidence such as diffusion and Brownian motion supports it.
It can't explain colour, reactions or electricity, because its particles are plain balls with no parts.
Every model has a scope and limits. Scientists keep a model for what it does well and use or build other models for the rest.
For teachers
Students identify what the particle model explains well and what it can't, reason from its assumptions to its limits, and name evidence for it (AC9S7U05, node 5). About 15 minutes.
I can name something the particle model explains well, and why.
I can name something it can't explain, and why.
I can give evidence for the particle model.
Before class
A short concept tutorial to close the particle theory unit, before Pure substance or mixture? Set the width with ?width=minimum, typical (default) or wider.
Not a hinge node. The progression asks for reasoning, not a list of limits: "what does the model assume, and what does this phenomenon need that the model doesn't have?" The sentence starter in "In your own words" scaffolds it.
Board notes: the diffusion board is the same as in Why can you squash air but not water?; here it stands for a prediction the model gets right.
Running the lesson
Engage: ask the students who chose 'throw it away' what they would use instead for squashing gases.
Explain: the sort is the success criterion; the reactions question is the reasoning.
In your own words: one 'explains well' and one 'can't explain', each with a reason that starts from the model's assumptions.
The hard part (on purpose)
Giving a reason for a limit, not just naming one. When a student writes 'it can't explain colour', ask 'what would the particles need to have for the model to explain it?'
When students get stuck
A student says a model with limits is wrong. Ask: Is a street map wrong because it doesn't show hills? Fix: No, it is built for a job. Models are judged by what they explain and predict.
A student lists limits without reasons. Ask: What does the model say particles are like? Fix: Plain moving balls that attract. Anything that needs particles to have parts (colour, reactions, electricity) is beyond it.
Stretch and support
Stretch: Particles in a solid are drawn touching, yet solids expand when heated. How does the model explain that? (The particles vibrate more and push each other slightly further apart.)
Support: Give the sentence frame: 'The model explains … because it says particles … . It can't explain … because it says nothing about … .'
Where it leads
Next: Pure substance or mixture? (AC9S7U06). In Year 8 the particles get parts (atoms), which extends the model.
In class: Brownian motion with smoke in a cell or a video; a class list of 'explains well' and 'can't explain' to revisit in Year 8.
What each step is for
Engage: is the model wrong?: Students tend to think a model is either right or wrong; 'useful for some things, not others' is the idea to build.
Explore: a prediction that works: Testing a prediction the model makes (diffusion, faster in gases) shows what the model is good at before asking what it can't do.
Explain: scope and limits: Reasoning from what the model assumes (plain moving particles that attract) to what it can and can't explain turns 'limits' into an argument, not a list.
Mix it up: The model is judged by what it explains well. Squashing is a clear case of it working, to set against the cases where it cannot.
Elaborate: a better model: Seeing that the atomic model adds what was missing shows why scientists use several models.
Elaborate: how the idea grew: The long road from an idea to an accepted model shows that evidence, not argument alone, decides.
Now you can
Name something the particle model explains well, and why.