Polarity of Molecules
You may have heard the saying "likes-dissolves-likes". This refers to the solubility of one substance in another. Polar materials tend to be more attracted to and are more soluble in polar solvents. Nonpolar materials tends to be attracted to and are more soluble in nonpolar materials.
Polar molecules are those that possess regions of positive and negative charge. Water is an example of a polar material. The type of bonds it has, when coupled with its shape, gives one end of the molecule a slight positive charge (the hydrogen end) and the other a slight negative charge (the oxygen end). These charges are attracted to the charges on other polar molecules. Generally, molecules with oxygen atoms, nitrogen atoms, or ionizable groups (-CO2H and -SO3H) tend to be polar.
Nonpolar molecules are those that do not possess regions of positive and negative charge. Ethane is an example of a nonpolar material. The type of bonds it has, when coupled with its shape, leaves the molecule with no regions of charge. Generally, the more carbon and hydrogen atoms a molecule has, the less polar (more nonpolar) it will be.
Continue to read about how polarity relates to retention.