A Particle Model (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Revision Note
Exam code: 8465
Written by: Alexandra Brennan
Updated on
The Particle Model
What is particle theory?
The particle model represents all particles (atoms, molecules and ions) as small, solid spheres
This simple model can be used to explain:
The properties of solids, liquids and gases
Changes of state such as melting, boiling, freezing and condensing
Particle theory explains how matter changes state depending on the energy and forces present between the particles in the substance
The amount of energy needed to change from a solid to a liquid and from a liquid to a gas depends on the relative strength of the forces acting between the particles
The stronger the forces between the particles, the higher the energy needed for melting and boiling to occur
When a solid is heated:
The particles absorb thermal energy which is converted into kinetic energy
The particles vibrate more and as the temperature increases, they vibrate so much that the solid expands until the bonds break and the solid melts
On further heating, the now liquid substance expands more and some particles at the surface gain sufficient energy to overcome the intermolecular forces and evaporate
When the boiling point is reached, all the particles gain enough energy for the intermolecular forces to break and the molecules to escape as the liquid boils
Particle Model Limitations
Higher tier only
The simple particle model makes several assumptions that do not reflect the true nature of particles:
Assumption of the model | Why this is a limitation |
|---|---|
Particles are small solid inelastic spheres | Atoms, molecules, and ions are not solid or inelastic |
All particles are the same size | Different atoms, ions, and molecules vary in size |
No forces act between particles | Intermolecular forces exist between particles in real substances |
Particles are shown in two dimensions | Atoms, ions and molecules exist in three dimensions |
Diagrams are static | Particles are always moving or vibrating |
Examiner Tips and Tricks
Questions on particle model limitations usually ask you to give two limitations, and examiner reports show most students only manage one.
The most commonly missed limitations are:
The diagrams are 2D, not 3D
The diagrams don't show particle movement
Avoid simply saying "it's not accurate" or "it's too simple". You must state specifically what the model fails to show.
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