Re: What if two Lewis structures for a molecule have the same formal charge?

Dear J.W.,
Please go to the following website to which I will be referring in order 
to help answer your question: http://dbh
s.wvusd.k12.ca.us/Bonding/Lewis-Structure-Rules.html
According to the rules, in particular #3, when drawing the 
structure: "Organize the atoms so there is a central atom SURROUNDED by 
ligand (outer) atoms".  In the case of O-O-S-O-O, half of the ligands are 
not surrounding the central atom (S). Therefore, according to the rules, 
the structure must be drawn such that the oxygens (all four) are truly 
around the S atom...As you know, when you follow the rules for (SO4)2-, 
the first structure has four single bonds (four S-O bonds) which is not 
correct (see rule #6) since the sulfur's formal charge is +2.  Rule #7 
then dictates that multiple (double) bonds must be drawn such that Rule #6 
is satisfied.  Therefore, the proper Lewis structure for (SO4)2- contains 
two S-O and two S=O bonds...
As for whether or not O-O-S-O-O could be a real molecule, probably not due 
to its instability.  That structure would be considered a "superoxide".  
Superoxides are compounds characterized by the presence of the (O2)- ion 
with an odd number (17) of electrons (Hawley's Condensed Chemical 
Dictionary, 12th Ed., 1993).  Most of them are unstable at room 
temperature with the exception of some metallic superoxides (for example, 
NaO2).    

Dan Berger adds:
The problem with the "surround the central atom rule" is that how would you
then draw C5H12? There are actually three perfectly good Lewis structures, 
which go by the common names of pentane, isopentane and neopentane. They have 
the structures (leaving off the hydrogens)

               C          C
               |          |
C-C-C-C-C    C-C-C-C    C-C-C
                          |
                          C
The thing that makes the O-O-S-O-O structure so unstable is not the fact that 
it's linear but the oxygen-oxygen bonds, which are not the most favorable thing 
for oxygen to do. But unless you know that fact, there really is no reason to 
prefer 

  O
  |
O-S-O    to     O-O-S-O-O
  |
  O