Year 7 · Science

Solids, Liquids and Gases: The Particle Model

5 checked activities 3 video matches

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.

Introductory comparison of the three states
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

A simplified model: it helps compare spacing and movement but does not show particles to scale.

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

Particles themselves do not expand, melt or change size when a substance is heated. Heating gives the particles more energy so they move faster and, in a gas, spread further apart.

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 particle arrangement in solids liquids and gases.

The activities include Explore the Different Particle Arrangement 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

Explore the Different Particle Arrangement in Liquids and Gases
Investigate the Movement of Particles in Solids, Liquids and Gases
Study the Differences Between the Three States of Matter
Understand the Arrangement of Particles in Solids, Liquids and Gases
Understand the Differences Between Solids and Liquids

Learning path

These same-subject links were reviewed as the foundations for this topic and the learning it directly unlocks.

Learn this first

Year 4Solids, Liquids and Gases: Year 4 Activities
Establishes the observable properties of the three states before particles are used to explain them.
Year 7The particle model: Year 7 KS3 introduction
Supplies the particle arrangement and movement used to explain shape, volume and compressibility.

Where this leads next

Year 7Changes of state with the particle model: Year 7
Applies these state properties to melting, freezing, boiling and condensing.
Year 7Diffusion: Particle Model
Uses particle spacing and movement to explain how substances spread and mix.

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