CIE IGCSE Chemistry

Revision Notes

1.1.1 Kinetic Theory

Solids, Liquids & Gases


  • Strong forces of attraction between particles, particles are packed very closely together in a fixed and regular pattern
  • Atoms vibrate in position but can’t change position or move
  • Solids have a fixed volume, shape and high density


  • Weaker attractive forces in liquids than in solids, particles are close together in an irregular, unfixed pattern.
  • Particles can move and slide past each other which is why liquids adopt the shape of the container they’re in and also why they are able to flow.
  • Liquids have a fixed volume but not a fixed shape and have a moderate to high density.


  • No intermolecular forces, particles are in random movement and so there is no defined pattern
  • Particles are far apart and move quickly (around 500 m/s) in all directions, they collide with each other and with the sides of the container (this is how pressure is created inside a can of gas)
  • No fixed volume, since there is a lot of space between the particles, gases can be compressed into a much smaller volume. Gases have low density

Exam Tip

Solids, liquids and gases have different physical properties. The difference in these properties comes from differences in how the particles are arranged in each state.

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.

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