is best described as a hybrid of the canonical or resonance forms I, II and III. In general, it may be stated that Resonance stabilizes the molecule as the energy of the resonance hybrid is less than the energy of any single cannonical structure; and, R e s o n a n c e a v e r a g e s t h e b o n d characteristics as a whole. Thus the energy of the O resonance hybrid is lower than either of the two cannonical froms I and II (Fig. .
). Many misconceptions are associated with resonance and the same need to be dispelled. You should remember that : The cannonical forms have no real existence. The molecule does not exist for a certain fraction of time in one cannonical form and for other fractions of time in other cannonical forms.
There is no such equilibrium between the cannonical forms as we have between tautomeric forms ( keto and enol ) in tautomerism. The molecule as such has a single structure which is the resonance hybrid of the cannonical forms and which cannot as such be depicted by a single Lewis structure. . .
Polarity of Bonds The existence of a hundred percent ionic or covalent bond represents an ideal situation. In reality no bond or a compound is either completely covalent or ionic. Even in case of covalent bond between two hydrogen atoms, there is some ionic character. When covalent bond is formed between two similar atoms, for example in H , O , Cl , N or F , the shared pair of electrons is equally attracted by the two atoms.
As a result Fig. . Resonance in CO – , I, II and III represent the three canonical forms. Fig.
. Resonance in CO molecule, I, II and III represent the three canonical forms. electron pair is situated exactly between the two identical nuclei. The bond so formed is called nonpolar covalent bond.
Contrary to this in case of a heteronuclear molecule like HF, the