Structure of sulfate

[Jessy Ji 2J]

So in the lecture on Oct 25 2021, professor showed us an example of sulfate structure and said it is more stable with two double bonds and lower formal charges. However, when do we know we need to modify a structure to make it more stable by including double bonds?

Thanks

[Jayden Arevalo 2B]

Hi Jessy, in class Dr. Lavelle stated that having less formal charges overall will result in a more stable compound. This is where resonance is key. Since multiple structures are able to be made, it is essential to think about the distribution of charges in the whole compound. The key is in just identifying when there is more than one possible structure and figuring out which results in less formal charges.

[Rachel Fox - 3F]

When making the Lewis structure for a molecule, we want to get the formal charge of each atom as close to 0 (which means that the molecule is more stable) as we can while still making the overall molecular charge (the sum of the formal charges) the charge of the ion. So, we would want to calculate the formal charge of each atom in the compound, and if the charges are separated (ie: less atoms have a 0 formal charge), then we might want to see if there is a possible structure of the molecule that could make it more stable and have less separation of charge.

[Jericho Ansay 1C]

Constructing Lewis structures is essentially a guess and check. For me, when determining whether to add double bonds to the structure, I add the double bond and see how it affects the other elements within the compound. If adding another bond overall changes the formal charge of the other atoms, then maybe adding that double bond is not the best option. Like you said, compounds are more stable with lower formal charges. If adding a double bond still results in little to no formal charge, then go ahead and include that double bond. Hope this makes sense!

[Kaya L]

I would always approach the lewis structure by finding the formal charge of the central atom since that is the atom that will be interacting with all the others. Usually, if the central atom is in a formal charge, the other atoms will follow suit smoothly. An example or trend I found, is always bonding C with 4 bonds. If C ever has lone pairs, it is usually not at a formal charge of 0, so you should add a double bond to it somewhere to turn the lone pairs into a bond.