CB13 Types of intermolecular forces

Aim: To give an overview of the most important intermolecular forces.

 

   We can differentiate between different intermolecular forces. These can be split into dispersion or London forces, multipole – multipole interactions (including dipole – dipole, dipole – induced dipole, dipole – quadruple interaction…), hydrogen bonding and ion-dipole interactions. On the illustration these are shown in order of increasing interaction energy.

The term Vanderwaals’ forces is frequently used to describe the intermolecular forces of attraction between neutral molecules, shown in the blue area of the illustration: if present these are always the dispersion forces + dipole – dipole and other multipole interactions.

The interaction energy of the hydrogen bond is mostly
~20 kJ mol-1, with HF2- (155 kJ mol-1) and HCl2-, HBr2- and HI2- (~ 50 kJ mol-1) as exceptions. This interaction energy is clearly lower than that of the “strong” chemical bonds (100-500 kJ mol-1) but higher than the “weak” Vanderwaals’ interactions
(0.1 – 5 kJ mol-1). Hydrogen bonds generate large, dynamic molecular aggregates that can be broken down without losing the identity of the basic molecule (e.g. in H2O). They play an extremely important role in determining the physical and chemical properties of the substance. The strength of ion-dipole interactions can be compared with that of hydrogen bonds.