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### Lewis Structures and Formal Charge

Posted: Sun Oct 23, 2016 8:16 pm
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

### Re: Lewis Structures and Formal Charge

Posted: Sun Oct 23, 2016 8:36 pm
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.

### Re: Lewis Structures and Formal Charge

Posted: Sun Oct 23, 2016 9:01 pm
I agree, I'd say stay safe and do both to make sure your lewis structure is perfect

### Re: Lewis Structures and Formal Charge

Posted: Sun Nov 05, 2017 4:35 pm
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.

### Re: Lewis Structures and Formal Charge

Posted: Sun Nov 12, 2017 10:30 pm
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.

### Re: Lewis Structures and Formal Charge

Posted: Sun Dec 03, 2017 10:18 pm
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!

### Re: Lewis Structures and Formal Charge

Posted: Sat Dec 09, 2017 9:14 pm
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.

### Re: Lewis Structures and Formal Charge

Posted: Sat Dec 09, 2017 9:44 pm
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.