Formal Charge equation?


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Giovanni Anguiano-Gutierrez 3L
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Joined: Thu Jul 25, 2019 12:17 am

Formal Charge equation?

Postby Giovanni Anguiano-Gutierrez 3L » Mon Oct 28, 2019 12:43 am

my TA was using the FC equation in class, but his differed to the one that Lavelle was showing in lecture. My TA used FC=V-(L+S/2*B) he stated that B is defined as bonding, but I was confused as to what we would use as an input for that variable B. Can anyone explain?

Bilal Pandit 1J
Posts: 98
Joined: Wed Sep 11, 2019 12:16 am

Re: Formal Charge equation?

Postby Bilal Pandit 1J » Mon Oct 28, 2019 2:21 am

I believe he is referring to the number of bonds that there are (the number of lines drawn on the Lewis structure for that specific atom.

Khushboo_3D
Posts: 60
Joined: Wed Sep 18, 2019 12:19 am

Re: Formal Charge equation?

Postby Khushboo_3D » Mon Oct 28, 2019 4:56 am

I think it might refer to the number of bonds, but I'm not entirely sure.

Robin Cadd 1D
Posts: 113
Joined: Thu Jul 11, 2019 12:16 am

Re: Formal Charge equation?

Postby Robin Cadd 1D » Mon Oct 28, 2019 7:51 am

I think your TA just used the textbook's equations. B stands for the number of bonding electrons on the atom.

Sean Cheah 1E
Posts: 105
Joined: Wed Sep 18, 2019 12:20 am

Re: Formal Charge equation?

Postby Sean Cheah 1E » Mon Oct 28, 2019 1:18 pm

Honestly, while memorizing the equation is fine and good, I like to tally up the number of electrons to subtract by simply counting each bond as one electron as each lone pair as two electrons. For example, if I saw a double bond, a single bond, and two lone pairs around a hypothetical atom, I could pretty quickly add up 3 electrons (1 from each bond) and 4 electrons (2 from each lone pair) to get a total of 7 electrons that I would then subtract from the number of valence electrons to get the formal charge.

AKatukota
Posts: 100
Joined: Thu Jul 25, 2019 12:18 am

Re: Formal Charge equation?

Postby AKatukota » Mon Oct 28, 2019 2:12 pm

The formal charge equation we were taught is

FC = V - (L + S/2)
where
FC = formal charge
V = valence e-
L = Long pair e-
S = shared e-


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