States of Matter

• Particle Model


  A model that describes the arrangement and movement of particles in a substance
• Particle Model


  • Can be used to explain the different states of matter e.g. solids, liquids and gases
  • Can be used to explain physical properties e.g. differences in density
• States of matter


  • Solid
  • Liquid
  • Gas
• Solid


  • Particles are closely packed
  • Particles vibrate about fixed positions
  • Have a definite shape (they are rigid)
  • Have a definite volume
• Liquid


  • Particles are closely packed
  • Particles can flow over one another
  • Have no definite shape – they are able to flow and will take the shape of a container
  • Have a definite volume
• Gas


  • Particles are far apart
  • Particles move randomly
  • Have no definite shape – they will take the shape of their container
  • Have no fixed volume – if placed in an evacuated container they will expand to fill the container
  • Highly compressible because there are large gaps between the particles and it is easier to push the particles closer together than in solids or liquids
• Differences in Density


  • Solids and liquids have tightly packed molecules, giving them a high density
  • Gases have widely separated molecules, giving them a significantly lower density than solids or liquids
  • At room temperature, the distance between molecules in a gas is roughly ten times (in each direction) the distance between molecules in a solid or liquid
  • The density of a gas is typically around one-thousandth (1/1000) of the density of a solid or liquid, e.g. the density of water is 1000 kg/m3, the density of air at sea level and room temperature is 1.3 kg/m3
• When a substance changes state, the number of molecules in that substance does not change, therefore its mass does not change
• Unlike chemical changes, physical changes like changes of state are reversible
• Solid


  • Molecules are very close together and arranged in a regular pattern
  • Molecules vibrate about fixed positions
• Liquid


  • Molecules are still close together (no gaps) but are no longer arranged in a regular pattern
  • Molecules are able to slide past each other
• Gas


  • Molecules are widely separated - about 10 times further apart in each direction
  • Molecules move about randomly at high speeds
• Changes of state


  • Melting
  • Boiling
  • Condensing
  • Freezing
  • Subliming
• Melting


  A solid turns into a liquid (e.g. ice to water) when energy is transferred to the system
• Boiling


  A liquid turns into a gas (evaporating) when energy is transferred to the system
• Condensing


  A gas turns into a liquid when energy is transferred away from the system
• Freezing


  A liquid turns into a solid when energy is transferred away from the system
• Subliming


  A solid turns into a gas when energy is transferred to the system