Chemistry (5070)
Topic 1 of 5Cambridge O Levels

States of Matter

Solids, liquids, gases and how particles behave

Everything around you is made of tiny particles (atoms or molecules). How these particles are arranged determines whether something is a solid, liquid, or gas.


Solids:

  • Particles are closely packed in a regular arrangement
  • Strong forces hold them together
  • They vibrate in fixed positions
  • Fixed shape and fixed volume
  • Example: Ice, salt crystals, steel

    • Liquids:

  • Particles are close together but in an irregular arrangement
  • Weaker forces than solids
  • Particles can slide over each other
  • No fixed shape (takes the shape of container) but fixed volume
  • Example: Water, petrol, cooking oil

    • Gases:

  • Particles are far apart, moving randomly at high speed
  • Very weak forces between particles
  • No fixed shape and no fixed volume
  • Can be compressed (squeezed into smaller spaces)
  • Example: Air, oxygen, CNG

    • Changes of State:

  • Melting (solid→liquid): particles gain energy, overcome forces
  • Boiling/Evaporation (liquid→gas): particles gain enough energy to escape
  • Condensation (gas→liquid): particles lose energy
  • Freezing (liquid→solid): particles lose energy, form regular pattern
  • Sublimation (solid→gas directly): e.g., dry ice, mothballs

    • Diffusion: Particles spread from high concentration to low concentration. Happens faster in gases than liquids because gas particles move faster.

    Key Points to Remember

    • 1Solids: fixed shape + volume. Liquids: fixed volume only. Gases: neither
    • 2Particles move faster as temperature increases
    • 3During state changes, temperature stays constant
    • 4Diffusion is faster in gases than liquids

    Pakistan Example

    The Ice Gola Vendor

    Watch an ice gola wala on a hot Karachi day: he shaves a block of ice (solid — particles vibrating in fixed positions) into fluffy snow. He adds sweet coloured syrup (liquid — particles flowing freely). As the gola sits in 45°C heat, the ice melts — particles gain thermal energy and start sliding over each other. If you leave it in the sun, the water eventually evaporates — particles gain enough energy to escape into the air as gas. One gola demonstrates all three states of matter!

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    Atomic Structure