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Lewis Structure(s)

Posted: Sun Nov 04, 2018 4:54 pm
by Isabel Nakoud 4D
On the exam, what if the question asks for the lewis structure of a structure that has resonance, but one of the structure has lower energy than the other 2 resonance structures?

For example, SO2

Technically, there are three resonance structures for SO2

However, one of the three structures (the structure with two double bonds) has lower formal charges than the other two resonance structures. So, if we were asked about this structure, should we draw all three resonance structures or just draw the one with the lowest formal charge?

Will the exam always clarify when to draw resonance structures and when to draw only one structure?

Re: Lewis Structure(s)

Posted: Sun Nov 04, 2018 5:08 pm
by Rachel-Weisz3C
I'm not sure if the directions will specify or not, but I would recommend writing them all out and drawing attention to the one with the lowest energy.

Re: Lewis Structure(s)

Posted: Sun Nov 04, 2018 5:13 pm
by whitney_2C
I believe that the exam will specify when to draw resonance structures. When it does ask you to draw resonance structures, it wants you to draw out the different possibilities for electron/atom arrangement where formal charges are closest to zero. This is kind of hard to put in words though so I attached a picture that will hopefully help. In the lewis structures, the two SO2 molecules have the same lowest formal charges for S and the Os the placement of the double bond is just different (which is what gives it resonance).

Re: Lewis Structure(s)

Posted: Sun Nov 04, 2018 6:56 pm
by Rami_Z_AbuQubo_2K
The exam will specify which formal structure it wants, which can include all 3. I believe that the more 0's there are, the lower the energy of that molecule but just know how to find the charges in general.