Rules For Writing Resonating Structures

Chemical Bonding of Class 11

Only electrons (not atoms) may be shifted and they may be shifted only to adjacent atoms or bond positions.
The number of unpaired electrons should be the same in all the canonical forms.
The positive charge should reside as far as possible on less electronegative atoms and the positive charge on the more electronegative atoms.
Like charge should not reside on adjacent atom
The larger the number of resonating structures greater the stability of the species.
A greater number of covalent adds to the stability of the molecule.