P1.3 Particle Theory and States of Matter

• What do we call the theory that attempts to explain the three states of matter?

  The particle theory.
• Use the particle (kinetic) model to explain how boiling occurs.

  1. As heat is applied to a liquid, the particles gain kinetic energy and move faster.
  2. With enough energy, the forces of attraction between the molecules will break.
  3. At this point, the liquid boils into a gas.
• Which state has the highest density?

  Solid.
• Use the particle (kinetic) model to explain how melting occurs.

  1. In solids, strong attractive forces hold the particles in place, so they can only vibrate in position.
  2. As the substance is heated, the particles gain energy and vibrate more quickly.
  3. Eventually, the particles have so much energy that they overcome forces holding them together, and the substance melts into a liquid.
• What is the particle (or kinetic) model of matter?

  It is a model that says that all matter consists of many very small particles that are constantly moving.
• Explain what will happen if you heat a gas in a fixed, closes container.

  The pressure will increase.

  When the gas is heated, the particles gain kinetic energy and move faster. If the gas is trapped within a container that cannot expand , it means that the volume of the gas is fixed, and so the pressure inside the container increases.
• Use the particles (kinetic) model to explain how condensation occurs.


  1. In gases, the particles have enough energy to overcome the attractive forces between them and so spread out randomly.
  2. If the temperature is lowered, they will no longer have enough energy to overcome these attractive forces, so the particles will move closer together and condenses into a liquid.
• What are the 3 assumptions of particle (or kinetic) theory?


  1. Small.
  2. Inelastic.
  3. Spheres.