Formal Charge SO42-

$FC=V-(L+\frac{S}{2})$

Mariam Baghdasaryan 4F
Posts: 37
Joined: Fri Sep 28, 2018 12:29 am

Formal Charge SO42-

The more stable structure of SO42- has 2 double bonds and 2 single bonds with O, but the single bonds have a formal charge of -1. Why can't those single bonds also become double bonds so that the formal charge becomes 0. Since S can accommodate more than 8 valence electrons, wouldn't this work?

Srikar_Ramshetty 1K
Posts: 64
Joined: Fri Sep 28, 2018 12:27 am

Re: Formal Charge SO42-

That's a great question. You want to make the most '0' formal charges to create the most stable structure in a molecule. However, the sum of formal charges should always equal the charge of the molecule. Therefore, adding double bonds to the other oxygen atoms will transfer make the FC on Sulfur -2, but since oxygen is more electronegative it would prefer having the electrons. Also SO4^2- will always have a formal charge sum of -2 since it has a charge of -2 so there is no benefit in continuing to add double bonds.

Hope that helps!

Mariam Baghdasaryan 4F
Posts: 37
Joined: Fri Sep 28, 2018 12:29 am

Re: Formal Charge SO42-

Thank you that makes sense!

404536963
Posts: 29
Joined: Fri Feb 02, 2018 3:02 am

Re: Formal Charge SO42-

After creating the Lewis Structure for the question, always do the formal charges around it to make sure that they are as close to 0 as possible! Even though it might look like it adds up and makes sense it may not be stable. In this example, the single bonded oxygens are unstable because they still have one unpaired electron, but if we were to double bond all of them, Sulfur would have a formal charge of negative two. Either way, one of the atoms will get the negative charge, but Oxygen's electronegativity makes it better suited to handle a single bond/ negativity.