Nonpolar vs Polar Covelant Bonding So I'm having trouble understanding the difference between the two. Looking specifically at water and carbon dioxide, CO2 is non-polar, because it is symmetrical and carbon shares two electrons with each oxygen and vice versa. But doesn't oxygen also share 1 electron with each hydrogen and vice versa? I know water isn't symmetrical, but for a molecule which I haven't seen the shape before how would I figure it out?
Look at each bond separately. In $CO_2$, in each $C=O$ bond, electrons are shifted towards oxygen atom as is has more pulling tendency(electron affinity). Now there is a formation of $\delta+$ charge on carbon and $\delta-$ on oxygen. This forms a dipole and you write it vectorially. In carbon dioxide, the vectors are equal and at $180$ degrees, so they cancel out and net dipole moment is 0, thus nonpolar molecule. Similarly, for the 2 $O-H$ bonds you get a net nonzero dipole moment, leading to a polar molecule.