materials and changing states

• Particle model of matter


  Everything is made up of lots of tiny particles
• Particle model


  • Can explain density and the three states of matter
• Density


  Measure of the compactness of a substance, relates the mass of a substance to the space it takes up
• The density of an object depends on what it's made of and how its particles are arranged
• A dense material has its particles packed highly together, a less dense material has its particles spaced out
• Three states of matter

  • Solid
  • Liquid
  • Gas
• Solids


  • Strong forces of attraction hold the particles close together in fixed arrangements, particles can only vibrate about their positions, highest density
• Liquids


  • Seek forces of attraction between the particles, particles can move past each other and form irregular arrangements, have more energy than solids, generally less dense than solids
• Gases


  • Almost no forces of attraction between the particles, particles have more energy than liquids and solids, free to move at high speeds, generally less dense than liquids
• To find the density of a solid object

  1. Measure mass

  2. Measure volume (if regular shape, calculate from dimensions; if irregular, measure volume of water displaced)

  3. Plug mass and volume into density formula
• To find the density of a liquid

  1. Place measuring cylinder on balance and zero

  2. Pour 10ml of liquid into cylinder and record mass

  3. Repeat for different volumes, calculate density for each

  4. Take average of calculated densities
• The volume of a cube is equal to length x width x height
• Internal energy


  The energy stored by the particles making up a system, in their kinetic and potential energy stores
• Heating a system


  Transfers energy to its particles, increasing their kinetic and potential energy, leading to a change in temperature or state
• A change of state conserves mass, the number of particles doesn't change, they're just arranged differently
• Changes of state


  • Melting
  • Boiling/Evaporating
  • Condensing
  • Sublimating
  • Freezing