Oxidation number formal charge compared

If one resonance form looks more like the resonance hybrid than the others, it weights the average in its favor. One way to select the more important resonance form is by determining each atom s formal chaise, the charge it would have if the bonding electrons were shared equally. Let s examine this concept and then see how formal charge compares with oxidation number. 

So far you have learned two different methods of electron bookkeeping. In Chapter 4, you learned about oxidation numbers [ W Section 4.4], and in Section 8.4, you learned how to calculate partial charges. There is one additional commonly used method of electron bookkeeping—namely, fonnal charge, which can be used to determine the most plausible Lewis structures when more than one possibility exists for a compound. Formal charge is determined by comparing the number of electrons associated with an atom in a Lewis structure with the number of electrons that would be associated with the isolated atom. In an isolated atom, the number of electrons associated with the atom is simply the number of valence electrons. (As usual, we need not be concerned with the core electrons.)... 

Formal charge and oxidation number. For the following species (a) locate all formal charges that are not zero, (b) determine the oxidation number of each atom, (c) compare the covalency of each atom having a formal charge with the normal value. Make a useful generalization based on your comparison. 

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