The electrons that contribute to an atom's charge are 1. All its unshared electrons 2. Polarization Bonds between non-identical atoms are very often polar i.e. the electron distribution in the bond is unsymmetrical. Some compounds are not adequately represented by a single Lewis structure. Dispersal of charge is stabilizing and concentration of charge is destablilizing.
Resonance hybrid is a mixture Look at acetic acid.
Resonance theory explains the stability of the conjugate anion and hence the wilingness of HOAc to loose a proton. General Rules for Resonance 1. All resonance structures must be valid Lewis structures 2. Structures differ only in arrangement of electrons. Atoms and bond angles cannot change.