Molecular Matter (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

• All molecules and matter are in motion at room temperature
  • The motion and arrangement of particles must be known for each state of matter
• In a solid:
  • The molecules are very close together and arranged in a regular pattern
  • The molecules vibrate about fixed positions

• In a liquid:
  • The molecules are still close together (no gaps) but are no longer arranged in a regular pattern
  • The molecules are able to slide past each other

• In a gas:
  • The molecules are widely separated - about 10 times further apart in each direction
  • The molecules move about randomly at high speeds

Properties of states of matter

Extended tier only

Intermolecular forces and motion of particles

• The forces between molecules and matter (or 'particles') affect the state of matter
• This is because the magnitude of the forces affects the relative distances and motion of the particles
• This affects the ability of the substance to
  • Change shape
  • Change volume
  • Flow
• The word particles can refer to:
  • Atoms
  • Molecules
  • Ions
  • Electrons

Solids

• The molecules in a solid are held in place by strong intermolecular forces
  • They only vibrate in position
  • The distance between them is fixed and is very small
  • This gives the solid its rigid shape and fixed volume

Liquids

• The molecules in a liquid have enough energy to overcome the forces between them
• They are still held close together
  • The volume of the liquid is the same as the volume of the solid
• Molecules can move around (by sliding past each other)
  • This allows the liquid to change shape and flow

Gases

• The molecules in a gas have more energy and move randomly at high speeds
  • The molecules have overcome the forces holding them close together
• Because of the large spaces between the molecules
  • The gas can easily be compressed and is also able to expand
  • Gases flow freely