Use particle theory to explain physical properties (how easily a substance squashes, its density, how it flows) by naming the arrangement, motion or attraction behind each one.
Seal the end of a syringe full of air and you can push the plunger a long way in. Do the same with water and it barely moves. Particle theory explains why, and the same explanation works for density, runny honey and smells crossing a room.
This lesson moves from describing particles to explaining properties with them. Every explanation names a particle feature: arrangement, motion or attraction.
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: three syringes
ExploreTry it on the board and compare what happens with your prediction.
Explore: push the plunger, count the particles
For each substance: push the plunger all the way in, then pull it back out and record how many particles sit in the dashed window. The window is the same size for every substance.
Try it yourselfNothing is saved: start again as often as you like.
Push the plunger all the way for wax, water and air, and record the window count for each.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: use the particles
In your book: explain two properties, why air can be squashed and why air is less dense than water. Check: did you name the arrangement, motion or attraction behind each one?
PractiseA few on your own, to check you have it.
Mix it up
Elaborate TypicalUse the same idea in a new context.
Elaborate: three substances
Honey, water and air. Which particle feature best explains each observation?
Honey pours much more slowly than water.Honey particles attract each other more strongly, so they don't slide past each other easily.
Air can be squashed but water can't.Air particles are far apart; water particles are already close.
Water is about 800 times denser than air.Water packs far more particles into each cm³.
The smell of honey spreads through a whole room.Smell particles keep moving and spread out between the moving air particles.
Warm honey pours faster than cold honey.Faster particles overcome the attraction more easily.
Elaborate WiderUse the same idea in a new context.
Elaborate: float or sink
Each window is 1 cm³. Iron particles are packed tightly and each one is heavier. Foam is mostly trapped air, so a window of foam holds very few particles.
Try it yourselfNothing is saved: start again as often as you like.
Elaborate WiderUse the same idea in a new context.
Elaborate: diffusion
Two colours of the same substance start on opposite sides of a barrier. When it lifts, they mix: this is diffusion. Predict first: will the gas or the liquid mix faster? Then time both.
Try it yourselfNothing is saved: start again as often as you like.
Time the mixing in the gas and in the liquid.
Use the board. This ticks when you get there.
Elaborate WiderUse the same idea in a new context.
Elaborate: mystery substance X
Try it yourselfNothing is saved: start again as often as you like.
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Which syringe did you predict would move furthest, and why? Write one sentence: "At first I thought… Now I think… because…"
Revision summary
Gases can be squashed because their particles are far apart, with lots of empty space between them.
Solids and liquids hardly squash at all: their particles are already close together.
Gases are much less dense because there are far fewer particles in each cm³. The same substance as a solid or a liquid has a similar density: its particles are close together in both.
The particles themselves never shrink or squash. Only the spaces between them change.
For teachers
Students use particle theory to explain physical properties (compressibility, density, viscosity), naming the arrangement, motion or attraction behind each (AC9S7U05, node 3, a hinge node for all of AC9S7U06). About 25 minutes.
I can explain why gases can be squashed and liquids and solids can't.
I can explain why a gas is less dense than a liquid using particle spacing.
I can name the particle feature (arrangement, motion or attraction) behind a property.
Before class
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider.
This is the hinge into pure substances and mixtures: every separation technique in AC9S7U06 is chosen by explaining property differences at the particle level. Students who can only label diagrams stall there.
Running the lesson
Engage: ask a student who chose water or wax to say why. Listen for 'the particles squash'.
Explore: the window count is the density idea. Point out that air's count is so low it is often 0 or 1.
Explain: insist on a particle feature in every sentence of the written explanation.
Follow up with real sealed syringes of air and water if you have them.
The hard part (on purpose)
Explaining with arrangement, motion and attraction, not the state's name. When a student says 'because it's a gas', ask what the gas particles are doing.
When students get stuck
A student says the air particles get squashed. Ask: Did any particle change size on the board? Fix: Particles never change size. The spaces between them get smaller.
A student says air is less dense because its particles are lighter. Ask: Count the particles in the window for air and for water. Fix: Spacing is the main reason: far fewer particles in each cm³. (A water particle is actually lighter than an average air particle.)
A student explains with state labels: 'because it's a gas'. Ask: What are a gas's particles doing that makes that happen? Fix: Name the feature: arrangement, motion or attraction.
Stretch and support
Stretch: Why does a bike pump get warm when you pump it hard? Use particle motion.
Support: Give the sentence frame: 'X can/can't be squashed because its particles are … so there is … space between them.'
Where it leads
Next: AC9S7U06 node 1, pure substances and mixtures at the particle level.
In class: sealed syringes of air and water; a density column of honey, water and oil.
What each step is for
Engage: three syringes: Committing to a prediction exposes the idea that particles themselves squash or shrink.
Explore: push the plunger, count the particles: The plunger tests compressibility; the fixed window turns density into something students can count.
Explain: use the particles: Two properties, each explained by spacing, with distractors built on the classic misconceptions.
Mix it up: Particles never change size: the same particles in a different arrangement explain the three states, and this lesson depends on it.
Elaborate: three substances: Honey and water share an arrangement but not an attraction: comparing three substances makes students choose the feature.
Elaborate: float or sink: Packing per cm³ links node 3's density to floating, a new context for the same idea.
Elaborate: diffusion: Diffusion is motion plus space: the same model predicts which state mixes faster.
Elaborate: mystery substance X: Predicting properties from a diagram, then checking real data, is the strongest test that students can use the model.
Now you can
Explain why gases can be squashed and liquids and solids can't.
Explain why a gas is less dense than a liquid using particle spacing.
Name the particle feature (arrangement, motion or attraction) behind a property.