Take #"CCl"_4#...each individual #C-Cl# bond is polar...and we could represent this as... #stackrel(""^+delta)C-stackrel(""delta^-)Cl#.. HOWEVER, molecular polarity is the VECTOR SUM of the individual bond dipoles, and certainly, the geometric sum of the bond dipoles in this highly symmetric, tetrahedral molecule is a BIG FACT ZERO.... And hence #"CCl"_4# is NON-POLAR, whereas, #CHCl_3#, #"chloroform"#, is polar...given the bond dipoles here would give a resultant upon addition.
For another example, consider #PF_5#..would the bond dipoles sum to zero?
