Question

how do I determine if a molecule is polar or non-polar?
ex: N2, HF, H2O

Answer 1

You can determine bond polarity by comparing electronegativites. Electronegativity is the amount one atom will tend to hold onto its electrons and pull them closer, so if there are two atoms in a molecule and one is pulling all of the shared electrons more, it's polar.
Diatomic elements (N2 for example) are never polar, and pretty much every other bond is polar except C-H bonds.

In order to tell if the whole molecule is polar, you need to draw an accurate Lewis structure. For some molecules, there will be two polar bonds but they will cancel each other out (think like two equally strong kids playing tug of war), but in the case of H2O there is a lone pair on the O, making the other two bonds not actually cancel each other out, and making water polar.

Answer 2

ok thnx