What are the two things that determine whether a molecule is polar or nonpolar?

Answer 1

First, to determine if a given individual bond is polar, you need to know the electronegativity of two atoms involved in that bond. To find the electronegativities of all the elements, look at the periodic table (follow the link below this answer under Web Links). If the electronegativity of the two atoms has a difference of 0.3 or less, then the bond is non-polar. If the electronegativity difference is greater that 0.3 but less than 1.7, then the bond is polar.

Answer 2

Excuse the part about the link there, was helping someone else and that got in there some how.

Answer 3

I agree with most of what Kai has written but there is one other point that needs to be made. After the individual bonds are checked to see if there is a polar bond within the molecule, the next thing to check is the three-dimensional structure. A molecule can have polar bonds but still be non-polar as a molecule. For example, CO2 has two C=O polar bonds; however, it is a linear molecule and the polarities cancel out which makes the molecule as a whole non-polar. CCl4 is another one. The C-Cl bonds are polar but the molecule is tetrahedral and the individual polarities cancel so the molecule is non-polar. CHCl3 is polar but CCl4 is not for that very reason. The secret is to know the electronegativities as well as the three-dimensional shape of the molecule. Symmetry makes the molecule non-polar.