How do you know if a molecule is polar? Would CH2Cl2 be polar or non-polar?

Answer 1

A molecule is polar if it satisfies two points:
1. It must have a dipole (usually between the central element and a surrounding atom and this will be true if the two atoms have different electronegativities [EN]).
2. The molecule must NOT be symmetrical in three dimensions.
For example:
CO2 is not polar. There is a difference in EN between each O and C but CO2 is a linear molecule; therefore, the O=C cancels the C=O bond and the molecule o CO2 (O=C=O) as a whole is not polar.
CH4 is the same. There is an EN difference between C and H but each individual C-H bond polarity is canceled by the three others since CH4 is a tetrahedral molecule which is symmetrical in three dimensions.
CH2Cl2 is polar because it is tetrahedral BUT it isn's symmetrical since the C-H bond polarity for the two C-H bonds is not canceled exactly with the two C-Cl bond polarities.