The particle model

• a particle is a tiny bit of matter
• the particle model describes how particles are arranged
• physical change

  when a substance changes state or shape, or breaks into pieces, no new substances are made, many can be reversed. e.g. melting butter
• chemical change

  a change that produces one or more new substances, they may look or taste different and may be in a different state. e.g. steel rusting
• What happens to particles during change?

  the particles stay the same but their arrangement and movement change. e.g. when ice melts its particles begin to move around
• Particles in a chemical change

  particles break up and join together in different ways
• the smallest particles that make up a substance are called atoms
• How big are particles?

  Helium atoms are the smallest atoms at just (62x10^-12m)
• What are the forces between particles?

  Electrostatic forces of attraction between positive and negative charges, strongest in solids and weakest in gases
• Limitations of the particle model

  does not take into account:

  • the forces between particles
  • the size of particles
  • the space between particles
• Particles do not change in size during state or temperature changes
• Increasing temperature increases kinetic energy which causes particles to move faster and further apart
• The distance between particles is greater in gases than liquids as there is more room for them to move around
• Solids have strong electrostatic bonds between their particles making them hard and rigid
• When a substance melts it goes from solid to liquid state