Limitations of the Particle Model (OCR GCSE Combined Science A (Gateway)) : Revision Note

Limitations of the Particle Model

Higher Tier Only

Particle Theory

  • 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 substances are heated, the particles absorb thermal energy which is converted into kinetic energy

  • Heating a solid causes its particles to 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 force to break and the molecules to escape as the liquid boils

  • How particles behave when a substance changes state can be summarised on the following graph:

Heating & cooling curve for pure substance, IGCSE & GCSE Chemistry revision notes

Particles and state changes

Limitations of the Particle Theory

  • Particle theory considers all particles, irrespective of their state or chemical identity, to be small, solid and inelastic

  • It doesn’t consider the difference caused by different particles, such as atoms, ions or molecules or mixtures of all three

  • The theory also fails to consider the intermolecular forces that exist between different particles in different substances

Examiner Tips and Tricks

Remember that the horizontal sections of a heating / cooling curve represent phase changes during which the temperature doesn’t change as the heat energy is absorbed during the process of changing state.

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Stewart Hird

Author: Stewart Hird

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.

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