[dzoys]

i have this homework problem which entails drawing lewis structures for

SO2
SO3
SO3(2-)
SO4(2-)

i got them all wrong when i checked the answers and the reason being is that i can not tell when sulfur and oxygen will make a single or double bond.
if sulfur has unpaired electrons and oxygen has unpaired electrons after a double bond, why can i NOT bond the rest of the lone pairs? the octet isn't affected (or is that it?)

[dzoys]

SO2 with the linear shape,  sulfur forms a double bond with one oxygen but not the other. why?
sulfur has a lone pair and oxygen has 3. why do they not bond to leave sulfur with no lone pairs, and the outstanding oxygen can remain identical as the first with 2 bonding and 2 lone pairs?



also,
would SO3 have 3 resonance structures? i am thinking yes due to the fact that there are 2 other single bonds which rotate the one S:O double bond.


am i missing the fact that sulfur has 4 bonding domains, where 2 double bonds would conceptually collide?
is that even a fact?

[nj_bartel]

I believe for your purposes, you can consider sulfur as having valence 2.

[dzoys]

how can i do that when i am drawing a lewis structure? all valence e-'s need to be accounted for (which they accurately were) if i chance the valence then how would sulfur achieve 3 and 4 bonds in all 4 of the compounds i've listed?

i have a feeling it involves VSEPR in someway.. non-bonding domains. if both oxygen's has double bonds it would conflict with the geometry.

i hope this is true and it if it i need someone to point out where my logic needs tweeking.

[dzoys]

also, sulfur's ox.# is +4 in SO2 and SO3(2-).
obviously the balance is direct with the identical electron count, but only forms 3 bonds with a lone pair.

interestingly, sulfur's ox.# is +6 in SO3 and SO4(2-), again identical electron #
now as +6, it will form 4  bonds and leave no lone pairs.

i know i am missing something here. chances are that it is obvious! i never had issues with Lewis structures but examining these 4 compounds together has me questioning every move i make in drawing Lewis diagrams now.

[nj_bartel]

Yea, sorry, I responded too quickly.  I'll look at it again in a minute - rushing around my place doing things.

[nj_bartel]

 http://en.wikipedia.org/wiki/Sulfur_dioxide
 http://en.wikipedia.org/wiki/Sulfur_trioxide
 http://en.wikipedia.org/wiki/Sulfite
 http://en.wikipedia.org/wiki/Sulfate

[dzoys]

i appreciate your help but my confidence in lewis structures is destroyed.

that's what i get for trying problems on my own. 

it will come back to me, but i will have to wait until next semester to have a professor whom i can ask.

[enahs]

Lewis Structures do not represent the real molecule, they are just idealized structures to draw on paper. Yes some information can be gathered from them, and they are valuable. But they do not work for everything, so do not stress too much over it.