Everything is
made of pieces.
with a kettle and an ice cube.
All matter is made of particles.
Take a drop of water and imagine cutting it in half, then half again, and again, and again. You would not go on for ever. Long before you reached nothing, you would arrive at a single particle of water that cannot be split and still be water. Everything around you — the air, this page, your own hand — is built from countless particles like that, far too small to see even down the best microscope.
The whole of this lesson rests on one idea, the particle model: matter is made of tiny particles, and those particles are always moving. The hotter something is, the faster they move. That single picture explains why ice melts, why a kettle steams, why a smell drifts across a room. Keep it in mind and the rest follows.
The very same particles can be arranged three ways. Solid — locked together in a fixed shape. Liquid — touching but free to slide, taking the shape of the container. Gas — flung far apart, filling all the space they're given. Ice, water and steam are all water — the only thing that changes is how the particles are arranged and how fast they move.
There is a coldest temperature it is possible to reach — absolute zero, about −273°C. At that point the particles slow almost to a standstill and can give up no more energy. Nothing in the universe can be colder. Even the empty space between galaxies sits a few degrees above it.
Solid, liquid, gas — drawn as particles.
If you could shrink down small enough to watch the particles themselves, here is what the three states would look like. The particles are the same in each — only their arrangement and their movement change.
What stays the same
- The particles themselves — same size, same number.
- It is still the very same substance throughout.
- Mass is conserved: nothing is lost in a change of state.
What changes
- Arrangement — fixed grid, loose huddle, or scattered.
- Spacing — close-packed to far apart.
- Movement — vibrating, sliding, or flying free.
Water is strange: most substances shrink when they freeze, but water expands. Its particles lock into an open, six-sided pattern that takes up more room than the liquid. That is why ice floats, why pipes burst in winter — and why ponds freeze from the top down, leaving fish alive below.
Melting, boiling, and the names between.
Add heat and you give the particles energy to move faster and break apart; take heat away and they slow and settle. Each crossing has its own name, and they come in pairs — one going up the temperature, one coming down.
Adding heat
- Melting — solid to liquid (ice to water).
- Boiling / evaporating — liquid to gas (water to steam).
- Sublimation — solid straight to gas, skipping liquid (dry ice, frost vanishing).
Taking heat away
- Freezing — liquid to solid (water to ice).
- Condensing — gas to liquid (steam to droplets on a cold window).
- Deposition — gas straight to solid (frost forming on grass).
Heat a beaker of ice and watch a thermometer: the temperature climbs to 0°C, then stops and holds there while the ice melts, even though you're still heating. All the energy is going into breaking the particles apart, not into making them hotter. Only once it's all liquid does the temperature climb again. The same pause happens at the boil.
Carbon dioxide skips the liquid state at ordinary pressures — solid "dry ice" turns straight to gas. That's why it makes such dramatic fog on a stage and never leaves a puddle. It sits at −78°C, cold enough to give a nasty burn, so it's only ever handled with gloves.
Heat is the energy that moves the particles.
In a school lab the heat comes from a Bunsen burner; in your kitchen it comes from the hob or the kettle. Either way, the job is the same — pour energy into a substance and its particles move faster, until they have enough to change state. Pulling energy back out, with a freezer or a cold night, does the reverse.
The particle model also explains diffusion — why a smell spreads. Open a bottle of perfume in one corner and minutes later you can smell it across the room. The perfume particles, in constant motion, mix in among the air particles and wander outwards until they reach your nose. Heat the room and it happens faster, because every particle is moving more quickly.
Why does a balloon stay firm? Its gas particles are flying about and bumping the walls, millions of times a second. Each bump is a tiny push; together they make the pressure that holds the balloon out. Warm the balloon and the particles move faster, hit harder and more often, and the pressure rises — which is why a balloon left in the sun can burst.
There's a fourth state of matter, and it's the most common one in the universe: plasma. Heat a gas hot enough and its particles tear apart into charged pieces. The Sun, every star, lightning and a neon sign are all plasma — so most of the visible universe isn't solid, liquid or gas at all.
Name the states.
Here are the three particle pictures again, numbered. Pick a label below, then place it in the matching Pin slot. These are the arrangements you met earlier. Two of the labels are not states of matter at all — read carefully before you place them.
Match each label to its pin
If you cool certain gases to within a whisker of absolute zero, their particles all fall into the very same state at once and start to behave as a single thing — a Bose–Einstein condensate. Predicted in 1925, it wasn't made in a lab until 1995, seventy years later.
Name the change of state.
Fresh one. An ice cube on a warm plate turns into a pool of water — solid to liquid. What is the name of that change of state?
The particles in a solid.
Hotter means…
Ice, water and steam.
Why a smell spreads.
The pause in the melt.
Glass is one of the oddest materials of all — its particles are jumbled like a liquid's, not lined up like a solid's, even though it feels rock-hard. Scientists still argue about what to call it. The old story that old window panes are thicker at the bottom because the glass has "flowed" over centuries, though, is a myth.
Worth watching.
Two short films to watch alongside today's lesson — each shows you something the words and pictures can't.
The words from today.
- Particle model
- The idea that all matter is made of tiny particles that are always moving.
- Solid
- A state where particles are packed in a fixed arrangement and only vibrate on the spot, so the shape is fixed.
- Liquid
- A state where particles touch but slide past one another, so it flows and takes the shape of its container.
- Gas
- A state where particles are far apart and move quickly, filling all the space they are given.
- Change of state
- When a substance moves between solid, liquid and gas — such as melting, boiling, freezing or condensing.
- Diffusion
- The spreading of particles from where they are crowded to where they are sparse, as moving particles mix.
You can read the world as particles.
You learned that everything is built from tiny moving particles, and that how they're packed and how fast they move makes a solid, a liquid or a gas. You met the changes of state and their names, and you know that heat is just energy that makes particles move faster. Next time the kettle steams or the window fogs, you'll know exactly what the particles are doing. Florence, this is chemistry.
The particles in the air around you are not gentle. At room temperature an average air particle is moving at around 1,800 km/h — faster than a jet — colliding with its neighbours billions of times a second. The calm, still air in your room is, up close, a storm.
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