Comparing Bond Lengths of Diff Molecules/Ions

[Summer de Vera 2C]

Hi! How can you compare the bond lengths of two molecules/ions to each other if in each molecule the central atom has different bond lengths connected to the atoms (e.g. one atom connected by single bond and other connected by double) ? For example, in 2D.13 b) 7th Ed, it asks you to put SO2, SO3, and SO3^2- in order of decreasing bond length for SO. Besides SO3^2-, not all the bond lengths in the other two molecules are the same, so how can you decide which SO bond length is shorter?

[105114680]

The bond lengths in SO3^2- are not the same. The most stable structure has one double bond and 2 single bonds. However, SO3^2- has resonance and thus the actual SO bond length in this molecule is not determined by any one individual bond but rather a blend of all 3. Thus the SO bond length in SO3^2- would be larger than the SO bond length in both SO3 and SO2 (which are both only comprised of double bonds). Hope this helps!