States of matter

States of matter

The different states of matter can be explained using particle models of atoms and molecules.
- In a solid, the particles are all tightly packed in a rigid structure. They cannot move because of strong intermolecular forces but they can vibrate.
- In a liquid, these forces are slightly weaker. The particles stay in contact but they can move and flow. The liquid can change shape to fit a container.
- In a gas, the particles can freely move. They are spread out so the gas expands to fill any volume, and the forces between particles are very small.

Solids and liquids have high densities as atoms are tightly packed together. In gases, the density is much lower as the atoms or molecules are spread out.
Substances can change state through various processes.
- During these, mass is conserved as the number of particles doesn’t change.
- These are physical processes because they are reversible and the substance does not change.

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