Bonding v Intermolecular forces

Forces between molecules are called van der Waals forces. These forces are up to one tenth the strength of intramolecular bonds.

The strength of these forces determine a molecule’s physical properties, i.e. melting point and boiling point.

Strong intramolecular bonds:
  • Ionic (between positive and negative ions)
  • Metallic (between positive ion lattice and sea of delocalised electrons)
  • Covalent (between two nuclei and one or more pairs of shared electrons)
Weak intermolecular forces (van der Waals):
  • Dispersion forces (due to electrons being in constant motion and the forming of temporary dipoles)
  • Dipole-dipole forces (between polar molecules)
  • Hydrogen bonds (between polar molecules containing OH, NH or FH)
  • Ion-dipole attractions (between polar solvent water and dissolved ions)

All bonding is based on electrostatic attraction. However, all bonding involves a mix of the three type. A bonding triangle shows how many substances may exhibit bonding that is a combination of all three bond types.

 

 

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