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

Jan 12, 2017

The standard representation of ${\text{SO}}_{2}$ is as a bent molecule, with formal charge separation.

#### Explanation:

$\text{VSEPR}$ predicts that sulfur dioxide should be a bent molecule, where, to a first approximation, $\angle O - S - O = {120}^{\circ}$. 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 $\angle O - S - O = {119}^{\circ}$, 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.