Resonance

__**Resonance**__ Resonance is the condition shown by a molecule when the valence electrons can be arranged in two or more ways. The results are multiple atoms with nearly the same energy and an atomic nuclei position which is unchanging. The idea is for the placement of the atoms to be the same while the placement of valence electrons differ. Resonance is helpful because it creates stability through the delocalization of electrons.

Lewis (electron-dot) structures are helpful in writing resonance structures. Ozone is an example of a molecule with resonance. The only accurate way to describe the structure of ozone is to show both Lewis structures (as shown below) and then indicate that the true molecule is an average of those two resonance structures. To indicate that the structures shown are resonance structures, a double-headed arrow is used. The average resonance structure for Ozone is 1.5 covalent bonds.
 * __Resonance structures__**



The nitrate ion is another example of resonance. Here, three equivalent Lewis Structures are drawn. The average resonance structure for the Nitrate ion is 1.33 covalent bonds.



__**Resonance in Organic Molecules**__ The aromatic molecules are especially aided by resonance while describing their bonding. This group of molecules includes the hydrocarbon, benzene, C6H6. The carbon atoms bond in the shape of a hexagonal ring, with a hydrogen atom attached to each carbon atom. Each of the Lewis Strutures shown below have 3 C-C single bonds and three C=C double bonds. The resonance is established because the double bonds are in different places among the structures.



The arrangement of bonding in benzene gives special stability, enabling endless organic compounds to consist of the characteristic rings of benzene.

http://www.environmental-expert.com/articles/article316/965-A.jpg [|http://upload.wikimedia.org/wikipedia/commons/archive/2/2a/20070124185020!Nitrate_ion_resonance_structures.png] [|http://www.chemvc.com/~tim/Benzene%20Resonance%20Structures.jpg] //Chemistry: The Central Science, 9th Ed.//
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