Describe the structure of solids.

  1. Particles are fixed in a regular arrangement.
  2. Particles are very close together.
  3. Particles vibrate.
  4. Strong forces of attraction between the particles.

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Describe the structure of liquids.

  1. Particles are arranged randomly.
  2. Particles are close together.
  3. Particles are free to move in random motion (in all directions).
  4. Medium forces of attraction between the particles.

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Describe the structure of gases.

  1. Particles are arranged randomly.
  2. Particles are far apart.
  3. Particles are free to move in random motion (in all directions).
  4. Weak/no forces of attraction between the particles.

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Why do solids expand when heated?

Solids expand when heated because the particles gain more (kinetic) energy, and so vibrate more.

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What are the limitations of the 3D model?

  1. It can be confusing when there are lots of atoms.
  2. They don't show electrons.
  3. They are hard to draw.

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What is the particle model (or kinetic model)? Include its assumptions.

A simple model in which solids, liquids, and gases, can be represented as lots of particles. It assumes that all substances are made from small, inelastic spheres.

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What is condensation?

The process by which a gas turns into a liquid.

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What is melting?

The process by which a solid turns into a liquid.

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In terms of particles and forces, explain why heating causes a solid to turn into a liquid.

In solids, strong attractive forces hold the particles in place, so that they can only vibrate in position. As the substance is heated, the particles gain kinetic energy and vibrate faster and faster.


Eventually, the particles have so much energy that they overcome the forces holding them together, and the substance melts into a liquid.

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Which has the highest density - solids, liquids, or gases?

Solids, as the particles are closest together in solids.

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