AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The three states of matter: (HT only) explain the limitations of the particle theory in relation to changes of state when particles are represented by solid inelastic spheres which have no forces between them.
The simple particle model represents particles as solid, inelastic spheres with no forces between them.
Study notes
From the checked teaching notes for this specification point.
The idea
The simple particle model represents particles as solid, inelastic spheres with no forces between them. Real particles are not solid spheres; they are atoms, ions, or molecules with internal structures that can deform. Furthermore, the model assumes no intermolecular forces. In reality, attractive and repulsive forces exist between particles. Because the model omits these forces, it cannot explain why different substances require different amounts of energy to melt or boil, nor can it explain varying melting and boiling points, such as why ionic compounds have higher melting points than simple molecules.
What earns the marks
- State that the simple model incorrectly assumes particles are solid, inelastic spheres.
- Identify that real particles (atoms, molecules, ions) have internal structures and are not perfectly spherical or inelastic.
- State that the model incorrectly assumes there are no forces between particles.
- Explain that because real particles have intermolecular forces, the model cannot account for the specific energy required to overcome these forces during melting or boiling.
- Explain that the absence of forces in the model means it cannot explain why different substances have different melting and boiling points.
Common mistakes and how to put them right
Stating the model is completely useless.
Put it right by acknowledging it is a useful simplification for basic states of matter, but specify its limitations regarding forces and particle structure.
Confusing intermolecular forces with the bonds inside molecules.
Put it right by specifying that the model fails to show the forces between particles (intermolecular forces), not the covalent bonds within them.
Forgetting to mention the 'inelastic spheres' limitation.
Put it right: Explicitly stating that real particles can vibrate, deform, and have complex shapes, rather than being rigid, solid spheres.
Exam tips
- As this is a Higher Tier only concept, expect questions to ask you to evaluate the model or explain why it fails to predict specific melting points.
- Always link the limitation directly to a physical property; for example, link 'no forces between particles' to the inability to explain latent heat or varying boiling points.
Try the lesson
The start of the The three states of matter: (HT only) explain the limitations of the particle theory in relation to changes of state when particles are represented by solid inelastic spheres which have no forces between them. lesson, made from checked teaching notes for this specification point.
Have a go first
In the simple particle model, particles are represented as solid inelastic spheres with no forces between them. Which statement describes a limitation of this model when explaining changes of state?
Listen
The simple particle model represents particles as solid, inelastic spheres with no forces between them. Real particles are not solid spheres; they are atoms, ions, or molecules with internal structures that can deform. Furthermore, the model assumes no intermolecular forces. In reality, attractive and repulsive forces exist between particles. Because the model omits these forces, it cannot explain why different substances require different amounts of energy to melt or boil, nor can it explain varying melting and boiling points, such as why ionic compounds have higher melting points than simple molecules. A strong answer earns marks for these points. State that the simple model incorrectly assumes particles are solid, inelastic spheres. Identify that real particles (atoms, molecules, ions) have internal structures and are not perfectly spherical or inelastic. State that the model incorrectly assumes there are no forces between particles. Explain that because real particles have intermolecular forces, the model cannot account for the specific energy required to overcome these forces during melting or boiling. A common slip: Stating the model is completely useless. Instead, acknowledging it is a useful simplification for basic states of matter, but specify its limitations regarding forces and particle structure. Exam tip: As this is a Higher Tier only concept, expect questions to ask you to evaluate the model or explain why it fails to predict specific melting points.
See it
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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