there are 7 main types of non-covalent forces.Non-covalent Molecular Forces, http://chemwiki.ucdavis.edu/Organic_Chemistry/Organic_Chemistry_With_a_Biological_Emphasis/Chapter_02%3A_Introduction_to_organic_structure_and_bonding_II/Section_2.3%3A_Non-covalent_interactions

there are 7 main types of non-covalent forces.
http://chemwiki.ucdavis.edu/Organic_Chemistry/Organic_Chemistry_With_a_Biological_Emphasis/Chapter_02%3A_Introduction_to_organic_structure_and_bonding_II/Section_2.3%3A_Non-covalent_interactions

2.3A: Dipoles

To understand the nature of noncovalent interactions, we first must return to covalent bonds and delve into the subject of dipoles. Many of the covalent bonds that we saw in section 1.5 – between two carbons, for example, or between a carbon and a hydrogen –involve the approximately equal sharing of electrons between the two atoms in the bond. This is because, in these examples, the two atoms have approximately the same electronegativity.  Recall from general chemistry that electronegativity refers to "the power of an atom in a molecule to attract electrons to itself" (this is the definition offered by Linus Pauling, the eminent 20^th-century American chemist who was primarily responsible for developing many of the bonding concepts that we have been learning).

Quite often, however, we deal in organic chemistry with covalent bonds between two atoms with very different negativities, and in these cases the sharing of electrons is not equal: the more electronegative atom pulls the two electrons closer to itself. In the carbon-oxygen bond of an alcohol, for example, the two electrons in the s bond are closer to the oxygen than they are to the carbon, because oxygen is significantly more electronegative than carbon. The same is true for the oxygen-hydrogen bond, as hydrogen is slightly less electronegative than carbon, and much less electronegative than oxygen.