- Define and explain The Particle Model in your own words
- Use key terms such as particle accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
Everything around you — air, water, your desk — is made of particles far too small to see, and they never stop moving. This simple idea, the particle model, explains melting, boiling and even why smells travel across a room. In this chapter you will use particles to explain the behaviour of matter.
This lesson focuses on The Particle Model: meet the idea that all matter is made of tiny moving particles.
Meet the idea that all matter is made of tiny moving particles.
Key ideas
Particles are always moving
In the particle model, every substance is made of tiny particles with empty space between them, and the particles are in constant motion. The hotter the substance, the faster its particles move — heating does not make new particles, it makes the existing ones move more. This one idea explains expansion, diffusion and changes of state.
Changes of state are about energy, not new particles
When ice melts, its particles gain energy and break free from their fixed positions — but they are still the same water particles. The temperature stays constant during melting and boiling because the energy goes into loosening the particles rather than making them hotter. That is why a thermometer in boiling water reads 100 °C no matter how fiercely it boils.
Key term — particle: An extremely small piece of matter; everything is made of particles that are constantly moving.
Someone peels an orange at one end of the classroom, and a minute later you can smell it at the other end. Explain this using the particle model.
The orange releases tiny scent particles into the air. Both the scent particles and the air particles are constantly moving in all directions. The scent particles collide with air particles and gradually spread from where they are crowded (near the orange) to where there are none (your end of the room). This spreading is diffusion, and it happens faster in warm air because the particles move faster.
Answer: Scent particles diffuse through the air: constant random motion carries them from the high concentration near the orange to the low concentration across the room.
- Thinking particles are still in solids Even in a solid, particles vibrate about fixed positions. They only stop moving at absolute zero (−273 °C), a temperature nothing in everyday life reaches.
- Saying particles melt Particles do not melt, expand or shrink — the substance does. Heating makes particles move faster and spread out; the particles themselves stay the same size.
Practice
Particles are packed tightly in fixed positions and vibrate; they cannot move around, which is why solids keep their shape.
Gas particles are far apart and move rapidly in all directions, so they spread until they fill the whole container.
The fastest water particles escape from the surface into the air as a gas; this is evaporation.
Particles move faster when hot, so they spread and mix more quickly.
Quick check
Which of these best defines "particle"?
A liquid is heated in a sealed, rigid container and the pressure rises. Explain using particles.
A thermometer in melting ice reads 0 °C the whole time. Explain why the temperature does not rise.
- The Particle Model: meet the idea that all matter is made of tiny moving particles.
- Particles are always moving: In the particle model, every substance is made of tiny particles with empty space between them, and the particles are in constant motion.
- diffusion: The spreading of particles from an area of high concentration to an area of low concentration.
- Watch out for: thinking particles are still in solids