Electronegativity decides polarity of bond
Dipole moment decides polarity of molecule
eg., If a molecule has 3 bonds ( Trigonal planar ) , polarity of each
BOND will contribute to the overall polarity of the MOLECULE.
Each bond is a dipole (having positive charge at one end and negative charge at another )
Now let the dipole moment of first bond is P1 and that of second bond is P2 and that of third bond is P3
first we will add the dipole moments P1 and P2, for which we'll use
UNDER ROOT P1 + P2 + 2P1P2 cos theta [ where theta is the bond angle
between bond 1 and 2 ]
and lower is the bond angle between them, higher will be the dipole moment !
hope this helps you out, If you're not satisfied, feel free to ask again :)
P.S. the resultant of P1 and P2 will be added to P3 to get overall dipole moment of the molecule !