Two factors that determine whether a molecule is polar are the types of atoms in the molecule and the SHAPE of the molecule.
A polar molecule is a molecule with two opposing charges, one end of the molecule has a partial negative charge while the other end has a partial positive charge. This occurs because the molecule is not totally symmetric. The polarity of a substance is typically determined by the characteristics of its constituent atoms and the shape of the molecule. Polar molecules are usually bent or trigonal in shape.