Year 7 · Science
Solids, Liquids and Gases: The Particle Model
Apply the Year 7 particle model
Use particle arrangement and movement to explain an observed property, not only to name the state.
How does the particle model explain solids, liquids and gases?
In a solid, particles are close together and vibrate about fixed positions. Liquid particles remain close but move past one another. Gas particles are much farther apart and move rapidly, so gases fill containers and compress. Density depends on the substance. For the same substance, the gas state is normally much less dense because its particles are much farther apart.
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes the container's shape | Fills the container |
| Volume | Fixed | Fixed | Not fixed |
| Particle spacing | Close together | Close together | Much farther apart |
| Movement | Vibrate about fixed positions | Move past one another | Move rapidly in all directions |
Keep practising: Continue to Year 9 density, pressure and model limits · Use the Year 7 Science checklist
Understand the key idea
In a solid, particles are packed closely in fixed positions and can only vibrate, so a solid keeps its shape and volume. In a liquid, particles stay close but slide past one another, so a liquid keeps its volume but takes the shape of its container. In a gas, particles are far apart and move quickly in all directions, so a gas fills whatever space it is given and is easily compressed.
Five introductory states-of-matter questions
- Why does a solid keep its shape? Its particles are close together and vibrate about fixed positions rather than moving past one another.
- Why can a liquid flow while keeping the same volume? Its particles stay close together but can move past one another.
- Why does a gas fill its container? Its particles move rapidly in all directions with large spaces between them.
- Why is a gas easier to compress than a liquid? There is much more empty space between gas particles.
- What changes when ice melts? Particle movement and arrangement change, but the water particles keep the same identity.
Common mix-up
Heating does not make the particles themselves grow. When temperature rises, particles move faster on average; a gas can expand if its container allows it. During melting or boiling at constant pressure, a pure substance can absorb energy without its temperature rising.
Try this first
- Sort shape, volume and compressibility for each of the three states.
- Draw a particle diagram for a solid, a liquid and a gas.
- Explain why a gas can be squashed but a liquid almost cannot.
Ask: Why can you compress the air in a sealed syringe but not the water?
Year 7 learners practise describing particle arrangement and movement in solids, liquids and gases.
The activities include Compare Particle Arrangements in Liquids and Gases, Investigate the Movement of Particles in Solids, Liquids and Gases, Study the Differences Between the Three States of Matter, and related practice. The checked support below includes teaching, interactive, lesson, video. Open a resource in its provider's website and choose the format that best helps the learner explain the idea independently.
Activities covered
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- Compare Particle Arrangements in Liquids and Gases — support from BBC Bitesize
- Investigate the Movement of Particles in Solids, Liquids and Gases — support from BBC Bitesize
- Study the Differences Between the Three States of Matter — support from Oak National Academy
- Understand the Arrangement of Particles in Solids, Liquids and Gases — support from BBC Bitesize
- Understand the Differences Between Solids and Liquids — support from BBC Bitesize
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Watch it explained
watch a video explanation
What is the arrangement of particles in a solid, liquid and gas?
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Melting Particle Model
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Solids, liquids and gases - Solids, liquids and gases
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Learn it properly
lessons and teaching pages
Oak lesson slides: Solid And Liquid States
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Oak lesson slides: Particle Model Of Substances In The Gas State
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Solid, liquid, gas states and changes of state
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Solids, liquids and gases - KS3 Physics
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Melting Particle Model worksheet and quiz downloads
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worksheets away from the screen
Oak worksheet: Particle Model Of Substances In The Gas State
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Oak worksheet: Solid And Liquid States
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The Particle Model and States of Matter Worksheet
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