Page 1 of 1

### Formula Provided

Posted: Wed May 16, 2018 1:37 pm
Will the formula be provided for formal charge on the next test or is that something we ought to just have memorized?

### Re: Formula Provided

Posted: Wed May 16, 2018 2:06 pm
I'm not sure if it will be provided but I would memorize it just in case. Formal charge = [# of valence electrons] – [electrons in lone pairs + 1/2 the number of bonding electrons]

### Re: Formula Provided

Posted: Wed May 16, 2018 10:23 pm
There is also an easier way to tell. If you get the number of valence electrons and subtract the electrons "directly surrounding it", you will find the formal charge.

Ex: CH4
C: 4 valence electrons - 4 electrons around it = 0
H: 1 valence electron - 1 electron around it = 0

### Re: Formula Provided

Posted: Thu May 17, 2018 4:09 pm
Thank you!

### Re: Formula Provided

Posted: Thu May 17, 2018 8:48 pm
Just a follow-up question. What is the importance of the formal charge when it comes to drawing a Lewis structure?

### Re: Formula Provided

Posted: Thu May 17, 2018 9:40 pm
Formal charge can be used to determine if a structure is stable. In drawing lewis structures for tests, the correct answer would be a lewis structure of a molecule with the formal charge of 0 (or close to zero).

### Re: Formula Provided

Posted: Thu May 17, 2018 10:51 pm
In response to the question right above this one, the formal charge also lets you know which structure would be correct since there as sometimes multiple ways you could draw the structure. Since the correct structure is the one thats the most stable (or with the formal charge they give you in that instance), you can calculate the formal charge to make sure you're answering with the right one.