What is a polar molecule?

$\mathbb{C} {l}_{4}$ is a non polar molecule because even thought each bond is highly polar the bondrs are symmetrical arranged and so all four sides of the molecule are negative.
$N {H}_{3}$ is polar. The bonds between the N and the H are not highly polar but there is a positive density on all of the Hydrogens The unbonded pair of electrons on the nitrogen have a negative density. The structure of the molecule is such that the three bonded Hydrogen are in the same plane while the unbounded electrons are in a different plane than the Hydrogens this creates a non polar molecule.