The Three States of Matter Notes
Oxford AQA IGCSE Chemistry: Revision notes
Key facts
- The three states are solid, liquid and gas.
- Solids: particles regular, close, vibrating in fixed positions.
- Liquids: particles close and random, sliding past each other. Gases: far apart, fast and random.
- Changes of state are physical, and reversible.
- Melting and boiling take in energy; freezing and condensing release energy.
- Temperature stays constant during a change of state.
Particles in each state
Going from solid to liquid to gas, particles gain energy, move further apart and move faster.
The state of a substance depends on how strongly its particles attract each other and how much energy they have. Heating gives particles more energy; cooling takes energy away.
Solid
Liquid
Gas
| Solid | Liquid | Gas | |
|---|---|---|---|
| Arrangement | Regular, close | Random, close | Far apart, random |
| Movement | Vibrate in place | Slide past each other | Move quickly everywhere |
| Energy | Least energy | More energy | Most energy |
Solid
- Arrangement:
- Regular, close
- Movement:
- Vibrate in place
- Energy:
- Least energy
Liquid
- Arrangement:
- Random, close
- Movement:
- Slide past each other
- Energy:
- More energy
Gas
- Arrangement:
- Far apart, random
- Movement:
- Move quickly everywhere
- Energy:
- Most energy
Which state has particles that are far apart?
Changes of state
Melting, boiling, condensing and freezing change a substance's state without making a new substance.
A change of state is a physical change and can be reversed. Heating gives particles enough energy to overcome the forces between them, causing melting or boiling. Cooling lets the forces pull particles closer, causing condensing or freezing.
- 1
Melting
Solid to liquid
- 2
Boiling / evaporating
Liquid to gas
- 3
Condensing
Gas to liquid
- 4
Freezing
Liquid to solid
Then back to step 1
Which of these is a chemical change?
Energy and temperature
Melting and boiling take in energy; freezing and condensing release it, and the temperature stays constant during the change.
Energy is needed to overcome the forces holding particles together, so melting and boiling take in energy. When particles move closer, forces form and energy is released.
During the change itself the temperature stays constant because the energy changes the arrangement, not the temperature.
Melting
- Energy taken in
Boiling
- Energy taken in
Freezing
- Energy released
Condensing
- Energy released
Which change releases energy?
Try an exam question
Describe the arrangement and movement of particles in a gas, and explain what happens to their energy when a gas condenses.
[4 marks]
- [1]Particles far apart and randomly arranged.
- [1]Particles move quickly in all directions.
- [1]Condensing: particles lose energy and slow down.
- [1]Forces between particles pull them together; energy is released.
That's the notes covered.
Carry on to the next subtopic.