In my discussion, we were doing problems where we had to draw lewis structures given the molecular formula of various molecules. I found that there were multiple ways of drawing certain structures, so I assumed one of them would be the most favorable by looking at the formal charges. However, there were times when the formal charges were all zero for each of the alternate lewis structures I drew. How do we know which is the correct structure of a molecule if there is no difference in formal charges?
Thanks!
multiple lewis structures
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Re: multiple lewis structures
Hi! If there is no difference in formal charge on the individual atoms, and therefore no difference in the overall charge of the molecule, I think the lewis structures would be resonance structures. Therefore, both structures are correct and equally contribute to the correct average structure.
Re: multiple lewis structures
If multiple lewis structures have a formal charge of 0, then they're all equally likely to be a stable structure.
But in reality, the electrons are delocalized, so the structure would be an average of all of the lewis structures combined.
Hope this helps!
But in reality, the electrons are delocalized, so the structure would be an average of all of the lewis structures combined.
Hope this helps!
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Re: multiple lewis structures
If the formal charges were all 0 for the multiple resonance structures you drew, this means each resonance structure for the given molecule is degenerate meaning they're equal in energy and contribute equally to the actual structure of the molecule. Remember, the actual structure of a molecule is actually a blending/average of all the possible resonance structures, but resonance structures that are lower in energy and are more stable contribute more to the actual structure than other resonance structures.
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Re: multiple lewis structures
If all of the alternate lewis structures have no differences in formal charges then they will be equally likely. However, different structures can have different formal charges on the atoms with the same overall net charge. If this is the case, then you would first look at if any structure has all atoms with a formal charge of 0. If this is not the case, then you would look for a molecule with a negative formal charge on the most electronegative molecule, as this is the most stable.
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