Lewis Structure for sulfate

[Sean Phen]

Hi,
In the lecture #13, the professor was drawing the lewis structure for sulfate, SO4. I am confused how oxygen can form a covalent bond with sulfur when all 6 valence electrons for oxygen are used up in the 3 lone pairs. Where does the extra valence electron come from in order to form a bond with sulfur? I am not sure if that makes sense or not.

[Chem_Mod]

The lewis structure for SO4 should have an overall of charge of -2. Sulfur can form up to 6 bonds given that it has 6 valence electrons. Sulfur double bonds to two of the oxygen atoms (giving those oxygens a 0 formal charge) and single bonds to two other oxygen atoms (giving those oxygens a -1 formal charge). Oxygen cannot have an expanded octet. In this situation, the double bonded oxygens should have two lone pairs and the single bonded oxygens should have three lone pairs, satisfying the octet rule.

[Izamary Marquez 2H]

The lewis structure for SO4 should have an overall of charge of -2. Sulfur can form up to 6 bonds given that it has 6 valence electrons. Sulfur double bonds to two of the oxygen atoms (giving those oxygens a 0 formal charge) and single bonds to two other oxygen atoms (giving those oxygens a -1 formal charge). Oxygen cannot have an expanded octet. In this situation, the double bonded oxygens should have two lone pairs and the single bonded oxygens should have three lone pairs, satisfying the octet rule.

In the diagram Lavelle drew, there were double bonded Oxygens with three lone pairs... Did I draw this wrong or is that what he had? Because in that case... Oxygen would have an expanded octet.