Dipole-Dipole Interactions

           Some atoms have more affinity for electrons than do other atoms, based upon the size of the atom and the distance of its valence electrons from the positvely charged nucleus. This results in certain atoms (such as the halides, oxygen and nitrogen) selfishly hogging electron density in chemical bonds with carbon, and others donating electron density (such as metals). As a general rule of thumb, as you go up and to the right of the periodic table, the electronegativity, or the measure of an atoms affinity for electrons, increases. Thus, as you go up and to the right on the periodic table, you reach the bully elements such as fluorine, oxygen, and nitrogen who like to hog electrons. In the illustration below, carbon atoms are shown as "weaker" than fluorine atoms at pulling electron density from their chemical bond with carbon (important note: "atoms" not drawn to scale).

Electron hogs such as fluorine selfishly steal electron density from less electronegative atoms like carbon

          If there is a difference in electronegativity (a carbon attached to fluorine for example), a permanent dipole is created on a molecule. These dipoles, or separation of charge, allow for interaction with other molecules by aligning opposing charges with other molecules, and sticking to each other like little atomic-scale magnets.

          The carbon-fluorine bond, shown above, has a dipole because fluorine is a powerful electron withdrawing atom (with high electronegativity), and carbon is not (low electronegativity). Thus, most of the electron density of the bond resides on the fluorine, thereby creating on it a partially negative charge . On the electron-deficient carbon, the charge is partially positive. It is very important to understand how electronegative atoms attached to carbons form dipoles, as it is essential in the understanding of the reactivity of organic molecules.