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Resonance_Structures_rev - electrons The individual...

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Resonance Structures Posted by M.Mure (Jan28, 2008) Resonance Structures We will frequently encounter species in which there is more than one valid Lewis structures. e.g. CO 3 2- Lewis Structure #electrons available C 4 3O 18 2(-) 2 _____________ 24 Join all atoms with electron pairs C O O O 4 at oms w/ oct et s need for C 2e - 2 O 3 x 6 = 18 20 more We do not have enough -----> multiple bond All are valid Lewis structures. Which is correct?? - None We know from X-ray data that all C-O bonds are the same length. The real carbonate ion (CO 3 2- ) is a "hybrid" and cannot be represented by the usual Lewis notation. The three possible structures we have drawn are resonance structures. They all differ only in the position of electrons and are C O O O C O O O but why not et c C O O O -2/3 -2/3 -2/3
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interconverted by simply moving electrons. "arrow formalism" - a curved arrow () represents the flow of
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Unformatted text preview: electrons. The individual structures have no real existence. They are called resonance structures or contributing structures. Rules of Resonance Structures 1) Differ only in the position of electrons. Nuclei do not change positions. 2) Each contributing structure must be a valid Lewis structure. 3) Energy of real structure is lower than that of any of the contributing structures. 4) Major contributors have octets around all atoms and minimum charge separation. 5) Negative charges are best on the most electronegative atom and positive charges on the least electronegative atom. C O H H C O H H major e.g. H C CH O H H C CH O H e.g. best C O O O electrons move from areas of high electron density to areas of lower electron density....
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Resonance_Structures_rev - electrons The individual...

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