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When finding the different resonance structures, I am wondering which ones we actually include in the answer. For example, hydrogen phosphate has a structure that obeys the octet rule and another structure where it forms a double bond. The double bond can move between the three oxygens so that gives rise to 3 more resonance structures. Is the final answer the structures with the three resonance structures with the alternating double bond for the oxygen, or do I also include the original one without the double bond that obeyed the octet rule but had a positive formal charge on the central atom?
Usually, you want the formal charge to be on the outside atoms and not the central atom. So maybe just keep the resonance structures with the formal charge on the outside. Another rule that applies to formal charge is that the formal charge is found on the most electronegative atom of the molecule.
Austin Clack wrote:I know this is a pretty simple question but, how do we indicate resonance structures? Can we just draw the structures next to one another or is there a more formal indication?
I think one way to indicate resonance structures is to draw out one lewis structure. Then from there see if 1. the structure has double bonds that could be shifted around and 2. if the structure alternates between double and single bonds that could alternatively switch with one another. I know this my be confusing but I hope this helped.
In class, professor Lavelle indicated the presence of resonance structures by drawing them next to each other and putting a double ended arrow (<-->) between to show that the different Lewis structures are interchangeable. Beyond that, I don't think there's a more sophisticated way to show resonance that we need to know now.
When you make a lewis structure that has resonance you need to draw all the resonance structures with double-sided arrows between them, as the correct lewis structure for the molecule is actually a hybrid of them all and not any single one.
ariellasarkissian_3H wrote: Is the final answer the structures with the three resonance structures with the alternating double bond for the oxygen, or do I also include the original one without the double bond that obeyed the octet rule but had a positive formal charge on the central atom?
The three structures with different locations for the double bond with oxygen all have resonance. However the original one you mentioned without the double bond wouldn't have resonance since is is structurally different than the other three.
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