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Rules for determining most representative resonance form

# Rules for determining most representative resonance form -...

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Rules for determining most representative resonance form 1. The resonance form(s) with the least number of atoms with formal charge is (are) the  most preferred. 2. Resonance forms with low formal charges are favored over high formal charge. (e.g.,  ± 1 is favored over  ± 2). 3. Resonance forms with negative formal charge or most electronegative atoms are  favored. 4. Resonance forms with the same charge on adjacent atoms are not favored. For example, N 2 O has number of 2 ( 5 ) + 6 = 16 valence electrons or 8 pairs. We can draw  the three valid Lewis structures below, labeled A, B, and C: For each structure we can calculate the formal charges below on each atom:
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Unformatted text preview: A B C N 1 5 - 2 - ( 6 ) / 2 = 0 5 - 4 - ( 4 ) / 2 = - 1 5 - 6 - ( 2 ) / 2 = -2 N 2 5 - 0 - ( 8 ) / 2 = + 1 5 - 0 - ( 8 ) / 2 = + 1 5 - 0 - ( 8 ) / 2 = + 1 O 6 - 6 - ( 2 ) / 2 = - 1 6 - 4 - ( 4 ) / 2 = 0 6 - 2 - ( 6 ) / 2 = + 1 Examining the formal charges above we see that Formula C is less representative because it has a -2 charge, and formula B is less representative because it has a -1 charge on N and 0 charge on O. Oxygen is more electronegative and should get -1 charge, therefore Formula A is most representative....
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