Intermolecular Forces: Van der Waals

Intermolecular Forces: Van der Waals

Van der Waals Forces


  • Van der Waals forces are a type of intermolecular force that occur between atoms and molecules.
  • They are named after Dutch scientist Johannes Diderik van der Waals, who contributed to our understanding of these forces.
  • These forces are generally weaker than ionic or covalent bonds, but are significant in certain environments.


  • Van der Waals forces are categorized into two types: dispersion forces (also known as London forces) and dipole-dipole interactions.
  • Dispersion forces occur between all types of molecules, whereas dipole-dipole interactions only occur between polar molecules.

Dispersion Forces

  • Dispersion forces, or London forces, are temporary attractive forces that result when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles.
  • These forces are dependent on the molar mass of molecules: larger molecules, or molecules with greater molar mass, have stronger dispersion forces.

Dipole-Dipole Interactions

  • Dipole-dipole interactions occur when the positive end of a polar molecule is attracted to the negative end of another polar molecule.
  • These forces are only effective over a short distance and are dependent on the polarity of the molecule.

Induced Dipole-Dipole Interactions

  • These interactions, also known as Debye forces, occur between a polar molecule and a non-polar molecule. The polar molecule induces a dipole in the non-polar one, leading to attraction.

Van der Waals Forces and Physical Properties

  • Van der Waals forces have significant effects on the physical properties of substances, such as boiling and melting points.
  • Substances with stronger van der Waals forces generally have higher melting and boiling points as more energy is required to overcome these forces.

Understanding van der Waals forces is integral to the study of several scientific phenomena, such as the behaviour of gases and the structure of proteins. Knowledge about these forces aids in comprehending the nature of molecular interactions and their outcomes.