Understanding the particle model of matter is one of the biggest turning points in Year 7 science. Suddenly, everyday objects stop being mysterious. Ice melting, steam rising from a kettle, perfume spreading across a room — all of it becomes logical once particles are understood.
This page continues the learning journey from the main science homework hub and connects with topics such as chemical reactions, the periodic table, separation techniques, and diffusion. Everything links together once the particle model makes sense.
Particles are the tiny building blocks of everything. They are too small to see, even with powerful microscopes, but scientists know they exist because experiments consistently show predictable behaviour.
Every solid, liquid, and gas behaves differently because the particles inside them are arranged differently and move differently. That single idea explains an enormous amount of science.
These three ideas appear simple but explain melting, boiling, dissolving, diffusion, reactions, pressure, and even weather patterns.
Solids are the easiest state to visualise. Think of a brick, a book, or a desk. These objects keep their shape and volume. That behaviour comes directly from how their particles are arranged.
Imagine students standing shoulder to shoulder in a crowded classroom. They can move slightly but cannot walk around. That is similar to particles in a solid.
The strong forces between particles hold them together. This makes solids:
This explains why a metal spoon does not suddenly flow like water.
Liquids are more flexible. Water flows, juice pours, and oil spreads. The particles are still close together but not locked in place.
Picture students walking slowly around a classroom. They stay near each other but can move freely.
Because particles move around, liquids flow and take the shape of whatever holds them. However, they keep the same volume because particles are still close together.
Gases behave very differently. Air fills rooms, balloons expand, and steam spreads quickly.
Imagine students running around a playground in all directions. That chaos represents gas particles.
Because particles move freely and spread out, gases expand to fill containers. This explains why smells travel across rooms — a topic explored further in diffusion.
Particle theory is not just a list of facts to memorise. It is a way of thinking. Instead of asking “What happens?” students begin asking “What are the particles doing?”
When answering questions, always describe:
Changes of state are simply particles gaining or losing energy.
| Change | What Happens to Particles |
|---|---|
| Melting | Particles vibrate faster and break free from fixed positions. |
| Freezing | Particles slow down and lock into place. |
| Evaporation | Fast particles escape from the surface. |
| Condensation | Particles slow and come closer together. |
| Sublimation | Particles move directly from solid to gas. |
Drop food colouring into still water. Watch particles spread. This shows motion even when nothing looks like it is moving.
Place a balloon in warm water. It expands because particles move faster.
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Particle theory connects directly to:
When a solid is heated, its particles gain energy. This does not make the particles bigger. Instead, the extra energy causes particles to vibrate more strongly. Because they vibrate more, the space between them increases slightly. This small increase in spacing causes the solid to expand. Metals expanding on hot days are a classic example. Railway tracks include gaps to allow for expansion. Without those gaps, tracks could bend or break. This explanation is essential in exams because students often mistakenly say particles grow bigger. They do not. The spacing increases due to increased motion.
Gases have large spaces between particles. When pressure is applied, particles can be pushed closer together. In solids, particles are already tightly packed, leaving almost no space to compress. This difference explains why air can be squeezed into cylinders but a metal block cannot be easily compressed. The concept also helps explain how bicycle pumps work, why aerosols spray, and how breathing functions. Understanding spacing is the key to answering these questions correctly.
Evaporation occurs at the surface of a liquid and can happen at any temperature. Only the fastest particles escape. Boiling happens throughout the liquid and requires reaching a specific temperature called the boiling point. Students often mix these ideas. A puddle drying on a warm day is evaporation. Water bubbling in a kettle is boiling. Both involve particles gaining energy, but the location and energy levels differ significantly.
This happens because gas particles move rapidly and randomly. When perfume is sprayed, particles move away from the source and collide with air particles. These collisions cause spreading in all directions. Over time, particles spread evenly throughout the room. This process is called diffusion and is important in breathing, cooking, and even how smells warn us about danger like smoke or gas leaks.
In liquids, particles can slide past each other because forces between them are weaker than in solids. In solids, particles are locked into fixed positions. Flow requires particles to move freely, which liquids allow and solids do not. This explains why water pours, honey drips slowly, and rocks stay fixed. The strength of particle forces determines the behaviour.
Particles never completely stop moving unless reaching absolute zero, a temperature far colder than anything naturally found on Earth. Even in ice, particles still vibrate slightly. This idea helps students understand that motion is a permanent property of matter. Cooling reduces movement but does not eliminate it. This concept is important in physics and chemistry.