Dipole - Dipole Forces


Definition of Dipole - Dipole Forces

Dipole-dipole forces are attractive forces between the positive end of one polar molecule and the negative end of another polar molecule. Dipole-dipole forces have strengths that range from 5 kJ to 20 kJ per mole

More About Dipole - Dipole Forces

  • They are much weaker than ionic or covalent bonds and have a significant effect only when the molecules involved are close together
  • Dipole-dipole forces act between the molecules possessing permanent dipole
  • Ends of the dipoles possess “partial charges” and these charges are shown by Greek letter delta (δ)
  • Partial charges are always less than the unit electronic charge 1.6 x 10 -19 C
  • The polar molecules interact with neighbouring molecules
  • This interaction is stronger than the London forces but is weaker than ion-ion interaction because only
  • Partial charges are involved
  • The attractive force decreases with the increase of distance between the dipoles
  • The interaction energy is inversely proportional to distance between polar molecules
  • Dipole-dipole interaction energy between stationary polar molecules is proportional to 1/ r3 and that between rotating polar molecules is proportional to 1/ r6 where ‘r’ is the distance between polar molecules
  • Besides dipole - dipole interaction, polar molecules can interact by London forces also
  • Thus cumulative effect is that total intermolecular forces in polar molecules increase
  • Polar molecules have a partial negative end and a partial positive end
  • The partially positive end of a polar molecule is attracted to the partially negative end of another
  • In an ICl molecule the more electronegative chlorine atom bears the partial negative charge; the less electronegative iodine atom bears the partial positive charge
  • The partially positive iodine end of one ICl molecule is attracted to the partially negative chlorine end of another ICl molecule
  • Intermolecular forces are weak compared to the Intramolecular forces
  • the covalent bond present within HCl molecules is much stronger than the forces present between the neighboring molecules, which exist when the molecules are sufficiently close to each other
  • Dipole-dipole interactions are electrostatic interactions between permanent dipoles in molecules
  • The dipole-dipole interaction between two individual atoms is usually zero, since atoms rarely carry a permanent dipole