Intermolecular Forces
Ref. (p. 15 – 19 of textbook)
Intermolecular forces are chemical bonds that attract molecules to one another. They
determine the physical state (solid, liquid, gas) of the molecular substance.
London Dispersion Forces (weak: between all molecules)
 A weak attractive force between molecules due to the unequal distribution of
electrons around an atom’s nucleus. This allows for electrons from another atom to
be temporarily attracted to the nuclei of its neighbour atoms.
example:. gases at room temperature – methane gas

The accumulation of London dispersion forces make larger non-polar molecules from
liquids. example: gasoline
Dipole –dipole Bonds (stronger than London Dispersion Forces)
 These bonds hold polar molecules to one another.
 The partially positive side on one polar molecule attracts the partially negative side of
another polar molecule.
Hydrogen Bonds (strong dipole – dipole bond) ***MOST IMPORTANT IN BIOLOGY!!***
 The strongest intermolecular force of attraction.
 The strong polar bonds between H and O or N or F of other molecules cause a strong
negative and positive pole on molecules involving these elements.