One of the important isues related to molecules is whether they are polar. Most chemical bonds are polar [local] -- there is a separation between the center of the positive charge and that of the negative charge in the molecule. This separation usually is attributed to differences in electronegativity -- the ability of an atom to attract shared electrons in a bond.

In a molecule with more than one bond, the bonds will be polar -- even if only slightly so. The arrangement of the bonds determines whether or not the molecule is polar.

The most systematic way to determine whether a molecule is expected to be polar is to decide which symmetry properties [local] the molecule has.

Polar molecules interact with ions more than do nonpolar molecules. They interact with one another. All other things being equal, they will have higher boiling temperatures and larger heats of vaporization.