• a molecule’s biological function is determined by the physical three-dimensional shape that it possesses
  • the types of atoms involved, each with their own number of valence electrons, determine the kinds of bonds that exist between them
  • the electron pairs that exist in the molecular (covalent) bonds between atoms dictate the shape of a molecule
  •  a Canadian chemist (R. Gillespie) developed a theory called the valence shell electron pair repulsion theory (VSEPR) to help determine the shape of any particular molecule


  • ·         the polarity of an entire molecule is dependent on two things – the bond polarity and the molecular shape
  • ·         symmetrical molecules (like Figure 10 (a)) are non-polar, while asymmetrical molecules are polar in nature
  • ·         all molecules attract other molecules – these forces of attraction are called intermolecular bonds
  • ·         these are the bonds that are broken in a substance when it changes state from solid to liquid to gas
  • ·         there are three types of intermolecular bonds, or van der Waals Forces: 
  1. London forces – weakest of the three; exist between all atoms and molecules; occur between non-polar substances
  2. dipole-dipole forces – hold polar molecules together; positive side of one molecule with the negative end of another
  3. hydrogen bonds – strongest of the three; occur between a hydrogen of one molecule and a very electronegative atom of another neighboring molecule, such as nitrogen (N), oxygen (O), or fluorine (F)