You need to know what the shape of molecule is and then you may determine its polarity. Hence, excepting hydrocarbon, the non-symmetric molecules are polar, because of uneven distribution of charge, while completely symmetric molecules present a symmetric charge distribution.
The nonpolar molecules present the following symmetric shapes: tetrahedral, linear, trigonal.
The distribution of electrons in geometric arrangements influences the polarity of the molecules, deciding if the molecule is polar or nonpolar.
Polarity determining involves several stages, the first being the Lewis structure determining, which is then used to determine the shape of the molecule. The symmetric shapes have one central atom and no lone pairs, while non-symmetric structures have one central atom and one or several lone pairs.
If the distribution of the outside atom is symmetrical, then the molecule is polar, while if the distribution of the outside atom is non-symmetrical, then the molecule is nonpolar.