Fall 2012 Midterm Q5B

(Polar molecules, Non-polar molecules, etc.)

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Josephine_Tang_1N
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Joined: Wed Sep 21, 2016 2:57 pm

Fall 2012 Midterm Q5B

Postby Josephine_Tang_1N » Tue Nov 01, 2016 6:46 pm

This questions asks for Lewis structures of a few gaseous molecules to see if they would contribute to global warming.

Part (d) asks for SO2, which I drew S as the central atom double bonded with O on both sides - both O's and S have a lone pair in my drawing, which has zero formal charge on each atom.
The answer given in the course reader gives is as S single bonded to O on one side (-1 FC on the O) and double bonded to the other O (0 FC on this O), leaving the S with a FC of +1.

Is there a reason to why this Lewis structure is better than the one with zero formal charge across all of the atoms?

Luiza Karakhanyan
Posts: 6
Joined: Wed Sep 21, 2016 2:59 pm

Re: Fall 2012 Midterm Q5B

Postby Luiza Karakhanyan » Tue Nov 01, 2016 7:22 pm

SO2 is a molecule with a resonance structure:
http://bilbo.chm.uri.edu/CHM501/oldproblemsets/Image1344.gif
And it is indeed, often preferred to exceed the octet rule for the sake of formal charge, so the proper Lewsi structure is a hybrid of the two. But, I guess, for a dipole moment to be present a resonance structure is needed in this case.

Navarro_Bree_1D
Posts: 24
Joined: Wed Sep 21, 2016 3:00 pm

Re: Fall 2012 Midterm Q5B

Postby Navarro_Bree_1D » Fri Nov 04, 2016 9:30 pm

This problem wants to know which gases contribute to global warming. Gases with dipole moments contribute to global warming. These dipole moments do not have to occur in the most stable form of the gas. The Lewis structure of SO2 with a single bond and double bond is a better representation for this problem because although two double bonds are more stable, the single and double bond has a dipole moment. This specific resonance structure shows that SO2 contribute to global warming.


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