How is #"sulfur dioxide"# represented by VESPER? What is the shape of the molecule?

1 Answer
Jan 12, 2017

The standard representation of #"SO"_2# is as a bent molecule, with formal charge separation.


#"VSEPR"# predicts that sulfur dioxide should be a bent molecule, where, to a first approximation, #/_O-S-O=120^@#. Why?

There are 18 electrons to distribute in the molecule, where sulfur, as the LEAST electronegative atom, will be central.

A Lewis structure of #O=S^(+)-O^-# is reasonable, where from left to right as we face it, there are 6, 5, and 7 valence electrons. Since for a Group 16 atom, there should be 6 valence electrons for neutrality, the assigned electronic charges are consistent with the Lewis representation. Of course, the 2 oxygen atoms are entirely equivalent, and the resonance isomerism available to #O=S^(+)-O^-# does reflect this.

The actual #/_O-S-O=119^@#, which is only slightly compressed from the idealized trigonal planar geometry. The longer #S-O# bonds, and the more diffuse sulfur lone pair, tend to diminish the repulsive properties of the the sulfur lone pair.

Note that the alternative Lewis structure #O=S=O# is still bent (why?), and entirely consistent with the structural parameters I have advanced. #O=S^(+)-O^-# is the standard representation proposed in texts and in schools ot chemistry.