The particle model of matter
FoundationMatter is made of tiny moving particles; solids, liquids and gases differ mainly in particle arrangement, spacing and motion.
- All matter is made of particles
- Arrangement and motion explain solid, liquid and gas
- Diffusion shows particles are always moving
§Text Passage
1What hides inside a single drop of water? Scientists answer with the particle model: all matter is made of tiny particles far too small to see. The particles have spaces between them and never stop moving. With this model we can explain why solids, liquids and gases behave so differently.
2The three states differ in how their particles are arranged and move. In a solid the particles are tightly packed and can only vibrate in place, so the shape and volume stay fixed; in a liquid they are freer and slide past one another, so the shape follows the container; in a gas they are far apart and dart about at high speed in all directions, filling the container and producing gas pressure.
3The model explains countless everyday observations. Perfume sprayed in one corner soon fills a whole room because its particles spread by diffusion; ice melting into water and water boiling into steam both reflect changes in how particles are arranged and move; and a tyre feeling harder on a hot day comes from gas particles moving faster and striking the walls more forcefully.
4Engineers put the particle model to practical use: gaps are left between railway tracks and expansion joints are built into bridges to cope with metal expanding in the heat. By linking the invisible microscopic world with everyday phenomena, the model explains changes of state, diffusion and gas pressure, forming a vital foundation for studying chemical and physical changes later on.
1Summary 重點摘要
Matter is made of tiny moving particles; solids, liquids and gases differ mainly in particle arrangement, spacing and motion.
2Vocabulary cards Vocabulary
A tiny unit that makes up matter and cannot be seen by the naked eye.
Has a fixed shape and volume; particles vibrate around fixed positions.
Has a fixed volume but no fixed shape; particles can slide past one another.
Has no fixed shape or volume; particles are far apart and spread in all directions.
The spreading of particles from where they are more concentrated to where they are less concentrated.
The change of state from solid to liquid on heating.
The rapid change from liquid to gas throughout the liquid when heated.
The pressure produced when gas particles constantly collide with the walls of their container.
3Step by step Steps
- SolidIn a solid the particles are packed closely in an orderly pattern, held by strong attractions, and each can only vibrate slightly in place rather than move about freely. That is why solids keep both a fixed shape and a fixed volume — an ice cube or an iron nail never moulds itself to a container. On heating the vibrations grow fiercer until the attractions can no longer hold the particles in place, and the solid melts — the microscopic story behind every change of state.
- LiquidIn a liquid the particles stay close together but arranged irregularly, and they can slide past one another. Liquids therefore have no fixed shape — they take on the outline of the container — yet they keep a fixed volume: the same cup of water fills a wide glass or a narrow bottle in equal measure. When heated, the particles slide faster and some escape from the surface, which is evaporation; the way water or oil spreads to fit any container in daily life is exactly this fluidity at work.
- GasGas particles are far apart and move fast, striking the walls of the container constantly and thereby creating gas pressure. Gases have neither a fixed shape nor a fixed volume: they spread to fill the whole container, like steam or the mixture of gases in the air. Compress a gas into a smaller volume and the particles strike the walls more often, so the pressure rises — the reason a bicycle tyre feels hard as you pump it up.
- Heating rearranges, never resizesHeating never changes the particles themselves, only their arrangement and motion: ice melting and water boiling are particles gaining energy and breaking free of their old pattern. A metal expands on heating for the same reason — the vibrations intensify and the spacing widens — while the particles stay the same size, and the metal shrinks back on cooling. This explains the practical gaps left in railway tracks and the expansion joints built into bridges.
- Names of state changesEach change of state has its own name: solid to liquid is melting, liquid back to solid is freezing; liquid to gas is vaporisation, which covers both evaporation and boiling, and gas back to liquid is condensation. Remember that throughout these changes only the arrangement and spacing of the particles change — the particles themselves never do. Water that freezes into ice and then evaporates into vapour is still the same substance.
- Temperature and diffusionTemperature reflects how vigorously the particles move: the higher the temperature, the faster the particles. Diffusion therefore quickens with heat: a drop of ink spreads rapidly in hot water but only slowly in cold water. Solids and liquids diffuse too, just far more slowly — the smell of salted fish gradually seeping into nearby food is one example. Knowing how temperature and diffusion are linked helps you make better choices when cooking and storing food.
4Diagrams Diagrams
5Worked example Example
Example: why can perfume smell travel across a room?
- Perfume evaporates into gas particles
- Gas particles move in all directions
- Particles spread from higher to lower concentration
- The scent finally spreads evenly around the room
- Answer: This is diffusion. Once the perfume evaporates into gas particles, they dart freely in all directions, drifting from the concentrated corner towards emptier regions until everyone in the room can smell it — direct proof that gas particles never stop moving; the warmer it is, the faster they spread, which is why smells carry further in summer.
6Common mistakes Mistakes
7Quick check Quick check
Q1Which state has a fixed shape and fixed volume?
Q2Why can a liquid flow?
Q3What property of particles does diffusion show?
Q4Water vapour cools and turns back into tiny droplets. What is this change called?
Q5As temperature rises, what happens to the particles and to gas pressure?
8Recap Recap
- All matter is made of particles
- Arrangement and motion explain solid, liquid and gas
- Diffusion shows particles are always moving
- Heating changes particle arrangement and motion, causing changes of state
- Gas pressure comes from particles constantly hitting the container walls