properties of simple molecular substances

• what happens to particles in a solid?

  particles vibrate around fixed positions
• what happens to particles in a liquid?

  1. particles have increased velocity
  2. particles remain in contact with each other
• what happens to particles in a gas?

  1. particles are no longer in contact
  2. particles move around in random directions
  3. particles move at random speeds
• what happens to particles during melting?

  particles break free from their fixed positions
• what happens to particles during boiling?

  1. particles separate from each other
  2. forming bubbles of gas in the liquid
• why do simple molecular substances have low melting points?

  1. molecules are held together in the crystal by weak intermolecular forces between molecules
  2. small amount of energy is needed to overcome these forces
• why do simple molecular substances not conduct electricity?

  1. no free ions or electrons
  2. electrons can't move and carry charge
• why are there no free ions or electrons in simple molecular substances?

  electrons are fixed in covalent bonds in molecules