Formal Charge

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

Posts: 72
Joined: Wed Sep 18, 2019 12:18 am

Formal Charge

I'm confused on what the formal charge is. Is that the number that's superscripted next to the symbol for example Cl ^-? Can somebody also please explain to me which numbers go where in the equation for solving the formal charge? I was especially confused on where the S came from because what made sense to me ended up not being the right thing. Thank you :)

nehashetty_2G
Posts: 86
Joined: Thu Jul 25, 2019 12:15 am

Re: Formal Charge

So formal charge is different from ionic charge. Formal charge takes into consideration the bonding in terms of electrons for each individual atom in the compound. Therefore, Cl in a compound does not always have a formal charge of -1. It could also have a formal charge of 0. We don't have to know how people derived the formula for FC, therefore I recommend just remembering the components of the equation and practicing to see how it works out.

The example Lavelle used in class for SO4 2- and how the Formal charge changes for each atom in the compound depending on if it is in the form with all single bonds or single+double bonds demonstrates the FC concept very well, so I would recommend looking over that!

SajaZidan_1K
Posts: 56
Joined: Wed Sep 18, 2019 12:15 am

Re: Formal Charge

Formal charge can also help you determine whether or not a certain lewis structure is better than the other if there is more than one way to draw a lewis structure. The more stable the formal charge is, the better the lewis structure is.

Katherine Brenner 3H
Posts: 73
Joined: Wed Sep 18, 2019 12:18 am

Re: Formal Charge

Does anyone know where we could find an example of this in the textbook (please post a page number if possible)?

Thanks

Hannah Lee 2F
Posts: 99
Joined: Thu Jul 11, 2019 12:15 am

Re: Formal Charge

You can find an example of a question dealing with formal charge in Example 2B.4 (page 85)! There's also a short section devoted to formal charge that starts on page 84.