Formal Charge


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Anna Nordstrom 1A
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Joined: Fri Sep 25, 2015 3:00 am

Formal Charge

Postby Anna Nordstrom 1A » Wed Oct 14, 2015 4:16 pm

I know that FC=V-(L+ S/2) and that having a formal charge of 0 is the most stable. Sometimes you can make a lewis structure that has a FC of 0 or a different number. The ideal structure would be the one with the FC of 0 so does this mean that this is the most common way that the molecule is found in the real world? Or is this more of an illustration for chemists drawing the pictures to visualize what is happening. Thank you

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Re: Formal Charge

Postby Chem_Mod » Wed Oct 14, 2015 9:47 pm

If a molecule has more than one possible lewis structure, than that molecule is in resonance. The molecule does not exist in the form of one lewis structure (one resonance structure) or the other. The actual structure of the molecule is a weighted average of all of its lewis structures. How each resonance structure is weighted depends on how stable it is. The most stable resonance structure will be the major contributor and have a larger weight than a resonance structure of higher energy. Formal charge is a good method for figuring out which resonance structure(s) is/are the most stable and thus would be the highest contributors to the actual structure of the molecule. You are right that minimizing the formal charge creates the most stable lewis structures! So, the resonance structure(s) with a formal charge closest to zero will be the major contributor(s) to that molecule's structure.


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