Formal Charge of Ions

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

Sierra Cheslick 2B
Posts: 61
Joined: Fri Sep 28, 2018 12:27 am

Formal Charge of Ions

For an ion, for example SO4 2-, do you want the overall formal charge to be zero or 2-? I'm confused because I remember Dr. Lavelle mentioning that compounds are most stable with a formal charge of zero, but I also remember something about how you have to maintain the charge of the ion.

Gary Qiao 1D
Posts: 66
Joined: Fri Sep 28, 2018 12:26 am

Re: Formal Charge of Ions

I think Dr. Lavelle meant for the central atom of sulfur to have a formal charge of 0, but the overall formal charge to stay at 2-. For sulfur here, with 6 valence electrons, in the formula FC = V - (l + s/2), FC = 6-(0 +12/2), FC=0.

Letizia Ye 4F
Posts: 62
Joined: Fri Sep 28, 2018 12:28 am

Re: Formal Charge of Ions

The overall charge of the sulfate ion is 2-, but the central atom sulfur has a formal charge of 0 based on the FC = V - (L +S/2) formula.

Emilee Hosking 1D
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Joined: Fri Sep 28, 2018 12:17 am

Re: Formal Charge of Ions

Why would the central charge be different from the overall charge of the molecule? I'm having a difficult time understanding this concept

Summer de Vera 2C
Posts: 65
Joined: Fri Sep 28, 2018 12:16 am

Re: Formal Charge of Ions

Would you have to draw all the resonance structures of an ion/compound/etc. in order to determine the formal charge?

Annalyn Diaz 1J
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am

Re: Formal Charge of Ions

I think the central charge only contributes to the overall net charge of the atom, so as long as the charge of the central atom in addition to the other atoms equal the overall charge, it'll be fine because that's what you're looking for.

Max Kwon 1J
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Joined: Fri Sep 28, 2018 12:18 am
Been upvoted: 1 time

Re: Formal Charge of Ions

I believe if you add up all the formal charges, you get the charge of the overall compound/ion. Each individual atom can have a different charge

Nicholas Kull_3L
Posts: 30
Joined: Fri Sep 28, 2018 12:23 am

Re: Formal Charge of Ions

Unless the question states that it wants the resonance structure drawn, then technically you would not have to draw it to determine formal charge because you could just use the formula; however, is extremely helpful to draw it out to make sure you have the correct number of lone pair and shared electrons.

Lopez_Melissa-Dis4E
Posts: 66
Joined: Fri Sep 28, 2018 12:20 am

Re: Formal Charge of Ions

When it comes to formal charge your goal is for it to be zero (or closest to zero) because it represents the stability of the specific atom. That is why you take the formal charge of each atom present in your compound, to see if they are all formally charged to 0.

Emily Ng_4C
Posts: 65
Joined: Fri Sep 28, 2018 12:17 am

Re: Formal Charge of Ions

You want each individual atom to be as close to zero as possible, but the overall formal charges should add up to the charge of the molecule.