The Three States of MatterOxford AQA IGCSE Chemistry: Revision notes
Section 1
What are the three states of matter?
All matter can be classified into one of three states: solid, liquid or gas. Which state a substance is in depends on how strongly its particles attract each other and how much energy those particles have.
The state of a substance can be changed by heating (giving particles more energy) or cooling (taking energy away).
Section 2
How are particles arranged in each state?
| State | Arrangement | Movement | Energy |
|---|---|---|---|
| Solid | Regular, closely packed | Vibrate in fixed positions | Least |
| Liquid | Randomly arranged, close together | Move around each other, sliding past | More than solid |
| Gas | Far apart, random | Move quickly in all directions | Most |
As a substance moves from solid to liquid to gas, its particles gain energy, move further apart, and move faster.
Section 3
What happens during changes of state?
Changing state is a physical change, not a chemical one — no new substance is formed, and the change can be reversed:
- Melting: solid → liquid
- Freezing: liquid → solid
- Evaporating/boiling: liquid → gas
- Condensing: gas → liquid
Heating gives particles more energy, so they vibrate or move more and can overcome the forces holding them together, causing melting or boiling. Cooling removes energy, so particles slow down and the forces between them pull them closer together, causing condensing or freezing.
Section 4
What energy changes happen during a change of state?
Changes of state involve energy transfers:
- Melting and boiling/evaporating take in energy from the surroundings, because energy is needed to overcome the forces holding particles together.
- Freezing and condensing release energy to the surroundings, because forces between particles get stronger as they move closer together.
During a change of state itself, the temperature stays constant even though energy is still being transferred — the energy goes into changing the arrangement of particles, not into raising the temperature.
A common error is to say temperature keeps rising while a substance melts or boils. In fact, temperature stays constant at the melting or boiling point until the change of state is complete.
Must Know
- The three states of matter are solid, liquid and gas
- Solids: particles in fixed positions, vibrate only
- Liquids: particles close together but can move past each other
- Gases: particles far apart, move quickly and randomly
- Heating gives particles energy to change state; cooling removes energy
- Melting/boiling take in energy; freezing/condensing release energy
- Temperature stays constant during a change of state itself
That's the notes covered.
Carry on to the next subtopic.