Intermolecular forces are the forces that exist between 2 individual molecules. This is different from intramolecular forces, which are the forces that exist within a molecule (ie. ionic/covalent bonds).
Intermolecular forces are generally described by a general term, Van der Waals forces.
Dipole-dipole Force
– the attraction of a dipole on one molecule for the dipole of another molecule
– the strength of this force depends on the strength of the dipole
Example: HCl molecules have dipole-dipole forces between them
Ion-dipole Force
– the attraction of an ion (anion/cation) for a dipole
Example: NaCl dissolves in water because of ions in NaCl are attracted to the dipoles in the water molecule
Induced Intermolecular Forces
1) Ion induced dipole
– when an ion comes near a non-polar molecule, the ion can induce a dipole in the non-polar molecule
Example: In blood, Fe+2 carries oxygen
2) Dipole induced dipole
– when a dipole comes near a non-polar molecule, the dipole can induce a dipole in the non-polar molecule
Example: Oxygen dissolves slightly in water
London Dispersion Forces
– the only force that exists between 2 non-polar molecules
– ALL things have London forces
– temporary attractive force between atoms/molecules close to each other
– strength of the force depends on the size (number of protons) of the molecule, larger molecules have a stronger London Dispersion Force
Example: Methane (CH4) vs Octane (C8H18)
Hydrogen Bonding
– stronger than dipole-dipole force
– occurs when when a highly electronegative element (Ex. N, O, F) is bonded to hydrogen
– since the element is highly electronegative, it ‘takes’ the electron from the hydrogen
– another highly electronegative element from another molecule then binds to that hydrogen
Example: Hydrogen bonding between water molecules
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This article was written for you by Samantha, one of the tutors with SchoolTutoring Academy.