Intermolecular forces of attraction

• 3 types of intermolecular forces of attraction

  1. Instantaneous dipole - Induced dipole forces
  2. Permanent dipole - Permanent dipole forces
  3. Hydrogen Bonds
• Instantaneous dipole - Induced dipole Interactions

  • Present between all particles
  • Overall attraction tends to be weak
  • The only type of intermolecular forces of attraction to exist between non-polar molecules
• Factors affecting the strength of instantaneous dipole-induced dipole interactions

  • Number of electrons/Size of electron cloud
  • Surface area for molecular interaction
• Id-Id interactions (number of electrons/size of electron cloud)

  Larger electron clouds are more easily polarised than smaller electron clouds resulting in greater ease of formation of id-id forces.
• Id-Id interactions (surface area for molecular interaction)

  • Id-Id interactions are stronger in molecules with greater surface for molecular interactions, given the same number of electrons.
  • Straight-chained hydrocarbons have greater surface area for intermolecular interaction compared to branched isomers.
  • As branching increases, surface area for molecular interaction decreases.
• Permanent dipole-Permanent dipole

  • Polar molecules have permanent dipoles in their structure and tend to align such that the partially positive end of one molecule is near the partially negative end of another molecule.
  • Electrostatic attraction between the partially positive end and partially negative end results in permanent dipole-permanent dipole.