Bonding\

• Intermolecular bonds


  Bonds or attractions that form between one molecule and another
• How London dispersion forces arise

  1. Electrons move around and a temporary dipole is set up

  2. Positive dipole of one molecule is attracted to the negative dipole of another molecule
• Intermolecular forces


  Stronger in polar molecules
• CCl4 is non-polar
• Trifluoromethane (CHF3) is polar
• Bonds in order of decreasing strength

  • Covalent
  • Hydrogen
  • London dispersion forces
• Types of intermolecular bonds

  • London dispersion forces
  • Hydrogen
  • Dipole-dipole
• How to test if a liquid is polar

  See if it is attracted to a charged polythene rod
• Hydrogen bonding


  Occurs between molecules with a hydrogen joined directly to fluorine, oxygen or nitrogen
• Propane vs butane


  London forces are stronger in butane (higher molecular mass)
• Water vs hydrogen sulphide

  Water has higher boiling point due to hydrogen bonding (H2S has weaker London forces)
• CH3CH2OH vs CH2(OH)CH2OH


  CH2(OH)CH2OH is more viscous (more hydrogen bonds)
• Molecules of HF with masses of 40 and 60 can be found
• Ice vs water


  Ice is less dense than water due to the more open structure from hydrogen bonds
• Insects walking on water

  Hydrogen bonds make the water molecules join forming a 'skin' on the surface