Year 7 · Science

Changes of state with the particle model: Year 7

5 checked activities 5 video matches

What changes when a substance changes state?

A change of state is a physical change. The particles keep the same identity, while energy transfer changes their movement, spacing and the effect of attractions between them. The model is useful for explaining patterns, but the dots are not literal pictures of particles and their spacing is not drawn to scale.

Evaporation compared with boiling
Feature	Evaporation	Boiling
Where it happens	At the liquid surface	Throughout the liquid
Temperature	Can happen below the boiling point	Happens at the boiling point for the given pressure
What particles do	Some surface particles escape	Gas bubbles form throughout the liquid

Changes-of-state diagram linking solid, liquid and gas with melting, freezing, evaporation, boiling and condensation arrows — The particle identity stays the same during each physical change of state.

Keep practising: Use the Year 7 Science checklist

Understand the key idea

Melting, freezing, boiling and condensing are physical changes. The substance keeps the same particles, but energy transfer changes how quickly those particles move and how strongly they are held together.

Model answer: explain what happens when water boils

The particles gain energy and move faster. When enough particles have enough energy to overcome the attractions holding them together, bubbles of water vapour form throughout the liquid, not only at the surface. The bubbles contain water vapour, not air, and the particles remain water particles: they do not change identity. This is the throughout-the-liquid distinction shown in the evaporation and boiling comparison above.

Common mix-up

Particles do not disappear or become a new substance during a change of state.

Try this first

Name the starting and finishing states.
Decide whether energy is transferred into or out of the substance.
Describe how particle movement, spacing and attraction change.

Ask: What stays the same when ice melts, and what changes?

Year 7 learners practise melting freezing boiling and condensing explained.

The activities include Compare Chemical and Physical Changes, Recognise Changes of State: Freezing and Condensing, Recognise Changes of State: Melting and Boiling, and related practice. The checked support below includes video, teaching, worksheet, lesson. Open a resource in its provider's website and choose the format that best helps the learner explain the idea independently.

Activities covered

Compare Chemical and Physical Changes
Recognise Changes of State: Freezing and Condensing
Recognise Changes of State: Melting and Boiling
Understand Changes of State and Forces of Attraction
Understand The Movement of Particles in Changes of State

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
The three states must be secure before transitions between them are modelled.
Year 4Heating And Cooling
The observed melting, freezing and evaporation that the particle model now explains.
Year 7The particle model: Year 7 KS3 introduction
Supplies the particle arrangement and movement this page reasons with.

Where this leads next

Year 7Diffusion: Particle Model
Applies the same particle movement to mixing rather than to state change.
Year 7Energy transfer diagrams and energy stores
Energy transferred during a change of state is the question this page raises next.
Year 10 / GCSEPhysics: Matter
GCSE internal energy and state change extend this model quantitatively.

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