A study guide to the particle model of matter: how the arrangement, spacing and movement of particles explain the properties of solids, liquids and gases. It covers melting, freezing, evaporation, boiling, condensation and sublimation, why temperature stays constant during a change of state, diffusion, gas pressure and expansion, with check-yourself questions and answers.
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Curriculum: Texas grade levels (TEKS). We show specific outcome codes only where they have been verified against the official curriculum document.
Completed: The Particle Model and Changes of State
8th Grade students (typically ages 13–14) working on states of matter & materials. It is pitched at level 2 · standard.
This is a study guide, so there is no separate answer sheet; the 'Check yourself' questions include answers.
About 25 minutes. Short, regular sessions work best: two or three a week beats one long one.
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Try Density Calculations: Mass, Volume and Density.
Success TutoringWorksheets8th Grade · Science · States of Matter & MaterialsThe particle model says that all matter is made of tiny particles that are always moving. There are forces of attraction between the particles, and the amount of space between them depends on the state. Heating gives the particles more kinetic energy, so they move faster.
| Solid | Liquid | Gas | |
|---|---|---|---|
| Arrangement | Packed closely in a regular pattern | Close together, no regular pattern | Far apart, randomly spread out |
| Movement | Vibrate in fixed positions | Move around and slide past each other | Move quickly in all directions |
| Attraction | Strong | Weaker than in a solid | Very weak |
| Shape | Fixed shape | Takes the shape of its container | Fills its whole container |
| Volume | Fixed volume | Fixed volume | No fixed volume |
| Can it be compressed? | No (almost not at all) | Hardly at all | Yes, easily, because of the large spaces |
| Change | From → to | What happens to the particles |
|---|---|---|
| Melting | Solid → liquid | Heating makes particles vibrate so much they break free of their fixed positions |
| Freezing | Liquid → solid | Cooling slows the particles until attractions hold them in fixed positions |
| Evaporation | Liquid → gas (at the surface) | Faster particles at the surface escape, at temperatures below the boiling point |
| Boiling | Liquid → gas (throughout) | At the boiling point, gas bubbles form all through the liquid |
| Condensation | Gas → liquid | Cooling slows the particles so attractions pull them close together |
| Sublimation | Solid → gas | Particles escape straight from the solid without melting first |
| Deposition | Gas → solid | Gas particles join a solid directly, such as frost forming on a cold night |
Heating ice from −10 °C to 110 °C (at normal air pressure)
Answers: 1. Condensation. 2. Gas particles have large spaces between them, so they can be pushed closer together; the particles in a solid are already packed tightly. 3. The energy is being used to overcome the attractions between the particles (to break them out of their fixed positions), not to make them move faster. 4. Water vapor in the air touches the cold glass, cools down and condenses into liquid water. 5. Evaporation: some particles at the surface have enough energy to escape into the air as a gas, even below the boiling point. 6. Diffusion: the gas particles of the smell move randomly and spread out from where there are many of them to where there are fewer. 7. The particles do not expand. They vibrate faster and move further apart, so the rod expands. 8. Evaporation happens only at the surface, while boiling happens throughout the liquid (with bubbles); evaporation happens at any temperature, while boiling happens only at the boiling point.
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