Calculating formal charges


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Betty Wolkeba section 1L
Posts: 32
Joined: Fri Apr 06, 2018 11:05 am

Calculating formal charges

Postby Betty Wolkeba section 1L » Sat May 12, 2018 1:20 pm

Can someone explain how to calculate formal charges again? Or if there's another way aside from the equation we learned in class? And if we're trying to ionic element's lewis structure, do we had the charge to the number of electrons to the element/compound?

Eli Esagoff_1I
Posts: 38
Joined: Fri Apr 06, 2018 11:02 am

Re: Calculating formal charges

Postby Eli Esagoff_1I » Sat May 12, 2018 1:45 pm

The formal charge for each element is:

FC = VE (valence electrons) - LPE (lone pair electrons) - 0.5BE (half the bonding electrons).

Hope this helped.

Jade Corpus-Sapida 1G
Posts: 35
Joined: Fri Apr 06, 2018 11:02 am

Re: Calculating formal charges

Postby Jade Corpus-Sapida 1G » Sat May 12, 2018 6:01 pm

Theres another equation (which gives essentially the same answer) just in a different format:
FCelement=(# of valence e-)-(# of lone pair e- + 0.5(#bonding e-))

Vienna Cimetta 1L
Posts: 31
Joined: Thu Feb 01, 2018 3:01 am

Re: Calculating formal charges

Postby Vienna Cimetta 1L » Sun May 13, 2018 4:33 pm

I just think of it as 1. taking the number of valence electrons (which can be found on the periodic table) and 2. taking this number and subtracting the number of electrons surrounding the specific element (where a bond would only really be one electron). This way its only a two step calculation and a lot faster.

Salena Chowdri 1I
Posts: 66
Joined: Fri Apr 06, 2018 11:02 am

Re: Calculating formal charges

Postby Salena Chowdri 1I » Sun May 13, 2018 5:15 pm

To calculate the formal charge, subtract the sum of the total number of lone electrons and total number of bonds (0.5 x total number of bonded electrons) from the number of valence electrons of that specific atom. All the atoms FC should add up to the compounds overall charge. It is preferred to have the lowest absolute value of FC for individual atoms. Like for CO2 it is preferred that each atom had a formal charge of 0,0,0 versus have 0,-1,+1.

AshleyLamba1H
Posts: 30
Joined: Fri Apr 06, 2018 11:03 am

Re: Calculating formal charges

Postby AshleyLamba1H » Sun May 13, 2018 10:01 pm

I found this video about formal charges on Khan Academy very helpful: https://www.khanacademy.org/science/che ... structures


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