The three states
- Solids: particles are closely packed in a regular pattern and vibrate in fixed positions.
- Liquids: particles are close together but randomly arranged and can move around each other.
- Gases: particles are far apart, randomly arranged and move quickly in all directions.
Changes of state
- Melting and freezing happen at the melting point. Boiling and condensing happen at the boiling point.
- The amount of energy needed to change state depends on the strength of the forces between the particles. The stronger the forces, the higher the melting and boiling points.
- The nature of the particles (atoms, ions or molecules) and the type of bonding decide how strong these forces are.
Predicting states
- If the temperature is below the melting point, the substance is a solid.
- If it is between the melting point and the boiling point, it is a liquid.
- If it is above the boiling point, it is a gas.
Limitations of the particle model
- The simple model shows particles as small, solid, inelastic spheres.
- It does not show the forces between particles, the space between them accurately, or that particles may be atoms, ions or molecules of different shapes.
State symbols
- In equations, (s) means solid, (l) liquid, (g) gas and (aq) aqueous (dissolved in water).
- Example: NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq).
Key terms
- Melting point
- The temperature at which a solid turns into a liquid (and a liquid freezes).
- Boiling point
- The temperature at which a liquid turns into a gas (and a gas condenses).
- Particle model
- A model that explains the states of matter using the arrangement and movement of particles.
- Aqueous
- Dissolved in water, shown by (aq).
- Condensing
- A gas turning into a liquid.
- Freezing
- A liquid turning into a solid.
- State symbol
- A letter in brackets showing the state of a substance in an equation.