Learning a Rule of Thumb for Resonance Structures

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Mitchell Kaake 4D
Posts: 4
Joined: Fri Sep 28, 2018 12:29 am

Learning a Rule of Thumb for Resonance Structures

Postby Mitchell Kaake 4D » Sun Nov 18, 2018 6:38 pm

What is the easiest way to choose the most valid structure between two resonance structures that have the same formal charge all around and/or different formal charges all around? Thanks.

Cody Do 2F
Posts: 62
Joined: Fri Sep 28, 2018 12:23 am

Re: Learning a Rule of Thumb for Resonance Structures

Postby Cody Do 2F » Sun Nov 18, 2018 7:11 pm

Using the Formal Charge formula, you'd calculate the formal charge for each atom. You want the resonance structure that has the appropriate charge for the molecule (neutral, positive, or negative) AND that has each atom with a formal charge closest to 0. If things are looking quite similar to each other, I found it's helpful to refer to the number of bonds/lone pairs that molecules like to have (usually, those that meet these requirements are the most stable):

C : 4 Bonds, no Lone Pairs
H: 1 Bond, no Lone Pairs
O: 2 Bonds, 2 Lone Pairs
N: 3 Bonds, 1 Lone Pair
S: 2 Bonds, 2 Lone Pairs
X (AKA any other element): 1 Bond, 3 Lone pairs

Mitchell Kaake 4D
Posts: 4
Joined: Fri Sep 28, 2018 12:29 am

Re: Learning a Rule of Thumb for Resonance Structures

Postby Mitchell Kaake 4D » Sun Nov 18, 2018 7:56 pm

Thank you for the helpful response!


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