would any chemistry wizz's be able to help me out with this problem...?

 

i just don't see why the formal charge on the sulphur atom is zero, i thought i would be +3.

 

Thanks

 

Sarah

oops nevermind, i just can't add up to 12. *shame*

would any chemistry wizz's be able to help me out with this problem...?

 

i just don't see why the formal charge on the sulphur atom is zero' date=' i thought i would be +3.

 

Thanks

 

Sarah [/quote']

What do you mean with formal charge? Is this oxidation state? The oxidation state of the sulphur in the ion you show (sulfate) is +6. All oxygens have oxidation state -2. In reality, the charge distribution is not so dramatic. All oxygens have a slight negative charge and the central sulphur might have a certain positive charge. The total charge of the sulfate ion equals -2.

In your model, two oxygens are negatively charged, but in reality, all oxygens of the ion are similar and you cannot distinguish between them.

To obtain the formal charge of an atom in a compound : just count how many bonds there are + the number of free electrons. And compare that number with the number of valence electrons.

 

In his example S has six bonds (a double bond with oxygen counts for two.) and no free electrons. So a total of six. S, group VIa, so six valence electrons. 6 - 6 makes a formal charge of 0.

 

Oxygen had one bond with S, six free electrons, total is 7, but group VIa, so 6 - 7 is -1 => formal charge of oxygen.

 

Other oxygen had two bonds with S, four free electrons, total is 6, so formal charge of 0

 

The sum of all the formal charges is the charge of the compound. Here 0 + 0 + 0 - 1 - 1 = a total of -2. Correct, becouse SO4 is SO4 2-