Lewis Structures and Formal Charge

[Alexis Elliott 1J]

Hi guys,

I was wondering if for every Lewis Structure we draw if we have to calculate the formal charge to figure out how many bonds to put in. Do you always have to calculate the formal charge to see if your number of bonds is correct? Or if you have the right number of electrons in your structure it is safe to assume your Lewis Structure is correct.

Thanks!
Alexis

[Katrina_Galian 1J]

I was wondering the same thing, but I think the safe thing to do is to just calculate the formal charge to check your work.

[Roline Dahi 1J]

I agree, I'd say stay safe and do both to make sure your lewis structure is perfect

[Yizhou Liu 3L]

Not always. For those simple Lewis structures such as CH4 and NH3, we know that the formal charge would be 0 and there's only single bond in those molecules. However, for those exceptions to octet rule, such as SO4^2- and ClO4^1-, you need to calculate the formal charge because they have expanded valence shells.

[Veronica Rasmusen 2B]

There are many cases where you will draw the most stable lewis structure right off the bat, but it's always a good idea to check formal charge in case just so you don't end up losing points.

[Sonja Kobayashi 1H]

Hello!
Even if the question does not ask you to find the formal charge, it is best to calculate it anyways because even though the lewis structure could have the right amount of bonds, that does not mean it is the most stable lewis structure. Therefore, you want to make sure the lewis structure you draw is the most stable meaning most of the formal charges are zero!

[Steven Chau 1B]

It would be best to calculate the formal charge just to check if your structure is stable. The lower the total formal charge of your compound the more stable it would be, so you would want to find the structure with a formal charge of 0.

[Angel R Morales Dis1G]

Yeah, check your formal charges to make sure the lewis structure makes sense. For example, if a Flourine in your structure ended with a positive charge, it's pretty clear that there is a mistake.