Particles and Their Behaviour
Particles and Their Behaviour
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Particles and Their Behaviour
Open with the idea that all matter is made of particles, but we cannot usually see them directly. The lesson will use the particle model to explain boiling, other changes of state, and diffusion.
Our learning goal
I can use the particle model to explain boiling, changes of state and diffusion.
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What words do you link with particles?
Use this to surface prior ideas such as tiny, moving, solid, liquid, gas, spread, hot, cold. Pick a few responses and connect them to the learning goal.
What is boiling?
Boiling is a change from liquid to gas
It happens throughout the liquid
Bubbles of gas form inside the liquid
For water, boiling happens at 100°C at normal pressure
Students often confuse boiling with evaporation. Stress that boiling happens throughout the liquid, not only at the surface.
Boiling in the particle model
Liquid particles are close together
Heating gives particles more energy
Particles move faster
Some particles spread out and become a gas
Keep the language simple: particles do not get bigger, melt, or turn into air. They gain energy and move more freely.
What stays the same?
When water boils, the substance stays the same. It is still water, but it changes state from liquid water to water vapour.
No new substance is made.
A common misconception is that bubbles in boiling water are 'heat' or 'air'. At boiling point, the bubbles are water vapour.
Reading boiling data
Temperature rises as water is heated
At the boiling point, the temperature stays steady
The energy is used for the change of state
The liquid changes into gas
If showing a heating graph in class, point out the flat section at 100°C for water. Students should link this to boiling, not to the heater being turned off.
Investigating the boiling of water
Use this slide to introduce the practical setup or a video of the practical. Mention measuring temperature over time and looking for when bubbling happens throughout the water.
What the investigation shows
As heating continues, the water gets hotter
At about 100°C, boiling begins
The temperature then stays about the same while boiling continues
This is evidence for a change of state
Keep this tied to interpreting data rather than practical method details, since the subtopic focus is on what the results mean.
What is inside the bubbles when water boils?
water vapour
oxygen
air
heat
Targets the common misconception named on the slides. The bubbles at boiling point are water vapour, not air or heat.
Boiling and data
When water is heated, its temperature rises. At about 100°C, boiling begins. While the water is boiling, the temperature stays steady because the energy is used for the change of state.
Echoes the wording from the boiling data slides: students should connect the flat temperature to boiling, not to heating stopping.
Boiling and evaporation
Both change a liquid into a gas
Boiling happens throughout the liquid
Evaporation happens only at the surface
Evaporation can happen below the boiling point
Useful contrast: a puddle dries by evaporation, not boiling. Students often think a liquid must reach 100°C to become a gas.
Changes of state involving gases
Evaporation / boiling: liquid to gas
Condensation: gas to liquid
Melting: solid to liquid
Freezing: liquid to solid
Keep the focus on naming and comparing states. Although melting and freezing are included, the key new idea here is the gas state and changes to or from it.
Condensation in the particle model
Gas particles are far apart and move fast
When gas cools, particles lose energy
They move more slowly
They come closer together and form a liquid
Link to everyday examples such as water droplets on a cold window or mirror.
State changes and particles
Heating → particles gain energy → particles move faster → state may change
Cooling → particles lose energy → particles move slower → state may change
This is a good summary chain. Emphasise that the particles themselves do not change into something else; their movement and spacing change.
Which statement compares boiling and evaporation correctly?
Both happen only at the surface
Boiling needs wind to happen
Evaporation happens at 100°C only
Boiling happens throughout the liquid
Checks the key contrast: boiling happens throughout the liquid, while evaporation happens only at the surface and can happen below boiling point.
State changes
When a gas cools, its particles lose energy and move more slowly. They come closer together and form a liquid. This change of state is called condensation.
Uses the particle explanation from the condensation and summary slides.
How is boiling different from evaporation?
Expected ideas: boiling and evaporation both change liquid to gas; boiling happens throughout the liquid; evaporation happens only at the surface; evaporation can happen below boiling point.
What is diffusion?
Diffusion is the spreading out of particles
Particles move from where they are more crowded
They spread to where they are less crowded
This continues until they are more evenly spread
Use a familiar example such as perfume spreading across a room. Avoid concentration terminology if the class is very low ability; 'more crowded' and 'less crowded' is acceptable at this level.
Diffusion in the particle model
Gas particles move quickly in random directions
They collide with each other
Over time, they mix and spread out
This is why a smell can travel across a room
If a video is available, show particle motion here. Random movement is important: particles are not choosing a direction.
Diffusion in liquids and gases
Diffusion happens in liquids and gases.
It is usually faster in gases because the particles move faster and are further apart.
This is a useful contrast slide. Students should connect particle spacing and speed to rate of diffusion.
What affects diffusion rate?
Temperature: warmer particles move faster
State: gases diffuse faster than liquids
Distance: shorter distances are quicker
Smaller, lighter particles usually diffuse faster
Keep explanations short and concrete. If needed, focus on the two core factors most likely required at Year 7: temperature and state.
Why heating makes diffusion faster
When particles are heated, they gain energy and move faster. Faster-moving particles spread out more quickly, so diffusion happens at a greater rate.
This slide links the diffusion subtopic back to the earlier work on heating and the particle model, helping the lesson feel coherent.
Extra questions
Boiling: liquid to gas
Condensation: gas to liquid
Evaporation happens at the surface
Boiling happens throughout the liquid
Diffusion is the spreading out of particles
Heating makes particles move faster
The user asked for an extra slide for extra questions, but this pass is content only. Use these as quick recap prompts orally if needed.
Why is diffusion usually faster in gases?
Particles are larger
Particles move slower
Particles move faster
Particles stop colliding
The nearby slides teach that gases diffuse faster because particles move faster and are further apart. Only one option is fully correct here.
Diffusion
Diffusion is the spreading out of particles. They move from where they are more crowded to where they are less crowded. Heating makes diffusion faster because particles move more quickly.
Closely matches the diffusion explanation on slides 12, 15 and 16.
Which part of this lesson do you feel most sure about now?
Boiling
Evaporation
Condensation
Diffusion
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What is one thing you learned today?
Reflection prompt. Invite short responses about one idea they will remember, such as boiling at 100°C, bubbles are water vapour, condensation, or diffusion being faster when heated.
Which part felt hardest today?
Reflection prompt. Encourage students to name a tricky idea such as boiling vs evaporation, reading the temperature data, or explaining diffusion with particles.
Glossary
particle model - a simple way to explain matter as tiny moving particles
boiling - the change of state from liquid to gas throughout the liquid
evaporation - the change from liquid to gas at the surface
condensation - the change of state from gas to liquid
diffusion - the spreading out of particles
water vapour - water in the gas state
change of state - when a substance changes between solid, liquid and gas
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