Everything Is Made of Particles

Introduction

If you could cut a drop of water in half, then in half again, over and over, would you ever reach a piece that could not be divided without stopping being water? Scientists answer yes. All matter is built from incredibly small pieces called particles . This single idea, the particle model , explains why solids, liquids and gases behave so differently, and it underpins almost everything else you will learn in chemistry.

Core explanation

The particle model makes a small number of simple claims about all matter.

1. All matter is made of particles. Every solid, liquid and gas is made of tiny particles. Depending on the substance, the particles may be single atoms (as in helium or iron), groups of atoms joined together called molecules (as in water, H₂O, or carbon dioxide, CO₂), or charged particles called ions (as in salt). At this level we simply call them all "particles" and draw them as small spheres.

2. Particles are extremely small. A single water molecule is about 0.3 nanometres across, where a nanometre is one billionth of a metre. A single drop of water contains roughly 1.7 × 10²¹ molecules, which is more than a hundred billion times the number of people on Earth. Particles are far too small to see even with an ordinary light microscope.

3. Particles are always moving. Particles in every state have energy of movement. In a solid they vibrate about fixed positions; in a liquid they slide past one another; in a gas they zoom about freely. They never stop completely.

4. There are attractions between particles. Particles pull on one another. These attractive forces are strongest when particles are close together, and they are what hold solids and liquids together.

5. There is empty space between particles. Between the particles there is nothing at all, not even air. In a gas the gaps are large; in solids and liquids they are small.

6. Particles of the same substance are identical. Every water molecule is the same as every other water molecule. Particles of different substances differ in size and mass.

The three states of matter are the same particles arranged and moving in different ways. Ice, liquid water and steam all contain identical water molecules; what changes is how close together they are, how strongly they are held and how fast they move. Heating gives particles more energy, which is why heating can turn a solid into a liquid and a liquid into a gas.

A model is not a perfect copy of reality. Real particles are not hard coloured balls, and they have no colour at all. The particle model is useful because it is simple, it explains a wide range of observations and it makes predictions we can test.

Step-by-step reasoning

To explain an observation with the particle model:

1. Identify the state or states involved. 2. Describe how the particles are arranged and how they move in that state. 3. Link the particle behaviour to what is seen, for example "particles moving randomly spread out, so the smell reaches the back of the room".

Visual explanation

Imagine zooming in on a glass of water, step by step, a thousand times each step. First you see the smooth liquid, then nothing new, until at the smallest scale you see a crowd of identical tiny spheres, touching, jostling and sliding past one another. The simulation shows these particles in motion.

Real-world analogy

A beach looks like a smooth golden surface from a cliff top, but close up it is made of countless separate grains of sand. Matter is similar, except that the "grains" are billions of times smaller and never stop moving.

Real-world example

When someone opens a bottle of perfume at the front of a classroom, people at the back soon smell it. The perfume particles escape from the liquid and move randomly through the air until some reach your nose. You cannot see the particles, but you detect them.

Why?

Why does sugar seem to disappear when it dissolves in tea? The sugar is still there, which is why the tea tastes sweet. Its particles have separated and spread out between the water particles, and individual particles are far too small to see.

Common misconception

"Particles in a solid are not moving." All particles move. In a solid they cannot change position, but they vibrate constantly about fixed points.

Worked example

Question: A sealed balloon has the same mass whether it is warm or cold. Use the particle model to explain why.

Reasoning: Mass depends on the number and type of particles. Warming makes the particles move faster, but no particles enter or leave the sealed balloon.

Answer: The number of particles is unchanged, so the mass is unchanged; only their speed changes.

Quick check

1. What is found in the spaces between particles? Answer: Nothing — the spaces are empty.

Exam focus

Learn the key statements: matter is made of tiny particles; particles are always moving; particles attract each other; there is empty space between them. When explaining any observation, refer to the particles explicitly and describe their arrangement and movement.

Advanced insight

The idea that matter is made of tiny indivisible pieces was suggested by the Greek thinker Democritus around 400 BCE, but it was only a guess. Strong evidence came much later: John Dalton's atomic theory in 1803 and Albert Einstein's 1905 explanation of Brownian motion, which convinced most scientists that atoms and molecules are real.

Summary

The particle model states that all matter is made of tiny particles that are constantly moving, attract one another and have empty space between them. Particles of one substance are identical. Solids, liquids and gases contain the same particles arranged and moving differently. The model is a simplification, but it explains a wide range of everyday observations.

Practice questions

1. State three main ideas of the particle model. Answer: All matter is made of tiny particles; the particles are always moving; there are attractions between particles (also: there is empty space between them). 2. How do the particles in ice compare with the particles in steam? Answer: They are identical water molecules; only their arrangement, spacing and speed are different. 3. Why can we not see particles with a school microscope? Answer: They are far too small, around a billionth of a metre across, much smaller than anything visible with light. 4. Use the particle model to explain how the smell of cooking spreads through a house. Answer: Particles from the food escape into the air and move randomly, spreading out until some reach people's noses in other rooms.