Everything on the GCSE Chemistry States of Matter & the Particle Model poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.
The three states
Solid - Strong forces of attraction hold particles close together in a fixed lattice arrangement. Particles vibrate about their positions. Solids have a definite shape and volume.
Liquid - Weak force of attraction between particles. Particles are randomly arranged and free to move past each other, but tend to stick closely together. Liquids have a definite volume and take the shape of their container.
Gas - Very weak force of attraction between particles. Particles are far apart and travel in straight lines with random motion. Gases have no fixed shape or volume and fill any container.
Changing state
Physical changes do not change the particles themselves, only their arrangement and energy.
- Melting and boiling (or evaporating) need energy to weaken and break the forces between particles.
- Freezing and condensing release energy as new bonds form.
- The stronger the forces between particles, the more energy is needed to break them - and so the higher the melting and boiling points.
Heating gives particles more energy and weakens the forces holding them together. Cooling lets new bonds form.
The changes of state are: solid → (melting) → liquid → (boiling/evaporating) → gas, and in reverse: gas → (condensing) → liquid → (freezing) → solid.
State symbols
State symbols are sometimes included in a balanced equation. They tell you the physical state of each substance.
| Symbol | State |
|---|---|
| (s) | Solid |
| (l) | Liquid |
| (g) | Gas |
| (aq) | Aqueous (dissolved in water) |
Example:
2HCl(aq) + CaCO₃(s) → CaCl₂(aq) + H₂O(l) + CO₂(g)
Aqueous hydrochloric acid + solid calcium carbonate → aqueous calcium chloride + liquid water + carbon dioxide gas