How are polar and nonpolar bonds alike?

Why can some molecules have polar bonds, but overall be nonpolar molecules?

• Why can some molecules have polar bonds, but overall be nonpolar molecules?

• Answer:

  The best way to see how this is possible is to consider the case of carbon dioxide, CO2. The chemical structure is as follows: O=C=O The C=O bond is polar because the oxygen atom is more electronegative than the carbon, thus attracting surrounding electrons more strongly than the carbon atom. You would expect the molecule to be polar, with a partial positive charge over carbon and a partial negative charge over each oxygen. However, keep in mind that the molecule has a linear shape. The carbon is in the middle and the two oxygens are located on either side, in the same plane. So even though the two oxygens are causing electron density to shift away from the carbon, creating dipole moments, they are pulling electron density in exactly opposite directions. As a result, the dipole moments cancel each other out. Simply put, the molecule doesn't have any overall polarity because the two polar bonds nullify each other's effect. This is how you can have polar bonds within a molecule, but have a non-polar molecule as a whole. I hope this helps! Good luck!