London Forces

• Also known as dispersion forces or Van Der Waals forces.
• It occurs between any type of substance or compound, but it mostly occurs between nonpolar covalent compounds (e.g., hydrocarbons) and monoatomic species.
• The weakest IMF.
• It occurs very temporarily (short period of time).
• •Occasionally, the electrons within an atom or molecule becomes distorted or skewed towards one direction. This forms a momentary dipole.
• Momentary dipole – an atom or molecule with a slightly partially positive charge and a slightly partially negative charge.
• A dipole is produced by that momentary dipole.
• Dipole-induced Dipole – dipole that is produced by a momentary dipole.
• Ion-induced Dipole – dipole that is produced by an ion (cation or anion).
• Larger atomic size of monoatomic species ⟶ Stronger London force
• Larger molecular size of nonpolar molecules ⟶ Stronger London force
• Examples of London Forces

  • N2 (Nitrogen Gas)
  • He (Helium)
  • CO2 (Carbon Dioxide)