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CHEMISTRY · Stage 7 · Chapter 1: The Particle Model and States of Matter

Chemistry 1.8 Chapter 1 Review: The Particle Model and States of Matter

5 min read 6 parts Lesson 8 of 8

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1.8 Chapter 1 Review: The Particle Model and States of Matter — Alhussan International Academy — Chemistry (Stages 7–9) notes: Revise the particle model, changes of state, heating curves and the limits of models from Chapter 1.Solid — the particles touch in a regular pattern and …

  • Properties
  • Physical changes
  • Evaporation
  • Key numbers
  • Puddle drying
  • Steamed-up window

Part 1 of 6States of matter and the particle model

  • Solid — the particles touch in a regular pattern and only vibrate.
  • Liquid — the particles touch but are arranged randomly and can slide past each other.
  • Gas — the particles are widely spaced, move rapidly in random directions and have very weak forces between them.
  • Properties — these arrangements explain shape, flow and compressibility.
    • Gases are easily compressed because of the empty space between particles.
    • Solids and liquids are almost incompressible.
  • Volumes — 1 g of liquid water has a volume similar to 1 g of solid water because the particles touch in both states.
    • Melting does not change the separation of the particles.

Part 2 of 6Changes of state

  • Physical changes — no new substances are made and the change is reversible.
  • Mass — it is conserved in every change of state.
ChangeFrom and toEnergy
MeltingSolid to liquidIn
FreezingLiquid to solidOut
Boiling or evaporationLiquid to gasIn
CondensationGas to liquidOut
  • Evaporationit takes place slowly at the surface at any temperature, whereas boiling happens throughout the liquid at the boiling point.
  • Speeding up evaporationhigher temperature, greater surface area, moving air and low humidity.
  • Key numberspure water melts at 0 °C and boils at 100 °C at normal pressure.

Part 3 of 6Explaining everyday events

  • Puddle dryingevaporation, as the faster surface particles escape from the liquid.
  • Steamed-up windowcondensation, as water vapour cools and its particles lose energy and come together.
  • Ice cube melting in a drinkmelting, with energy taken from the drink so the drink cools.
  • Description of a changename the change, say whether energy is taken in or given out, and describe particle movement before and after.

Part 4 of 6Heating curves and purity

  • Rising sectionsparticles gain kinetic energy.
  • Flat sectionsa change of state is taking place, and energy goes into overcoming forces between particles rather than raising the temperature.
  • Reading the graphthe temperatures of the flat sections are the melting and boiling points.
  • Puritypure substances have sharp melting and boiling points, while mixtures change over a range.

Part 5 of 6Models and their limits

  • Particle model — it is a simplification that works well.
  • Strength — it explains states, changes of state and diffusion.
    • Diffusion gives further evidence for the model because it shows that particles must be moving.
  • Limitations — real particles are not solid spheres, they move constantly, and diagrams cannot show forces or spacing to scale.

Part 6 of 6Precise vocabulary

  • Particles vibrate, move randomly, attract each other, and overcome forces when a substance changes state.
  • Particles themselves do not melt or get hot — they move faster or vibrate more strongly, but the particle is unchanged.

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