This charge separation within a molecule is called a dipole and the vector describing it is the dipole moment of the molecule. This is most easily seen in looking at the structure of Ammonia, NH 3 . The electron dot structure of ammonia shows that N needs four equivalent molecular orbitals. It affects the intermolecular forces than hold ammonia molecules to each other. We touched on this when we discussed phase transitions in thermodynamics.
Phase transitions are breaks in the heating curves.
These occur at characteristic temperatures for all compounds. A great deal of heat must be added to break them. Consequently, ionic species have very high melting and boiling points. Think of trying to melt NaCl. The relatively weak attractive forces between uncharged atoms or molecules are collectively called van der Waals forces.