Shortcut for Formal Charge

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

AryaG_4C
Posts: 50
Joined: Mon Sep 30, 2019 12:16 am

Shortcut for Formal Charge

Does anyone know any short method or trends that make it easier to know/calculate the formal charge of an atom? Like creating a double bond would help the formal charge to be more towards zero etc?

Akshay Chellappa 1H
Posts: 59
Joined: Wed Sep 11, 2019 12:15 am

Re: Shortcut for Formal Charge

From the chemistry review session on Friday one of the UA's showed us that you can draw a circle around one of the atoms and count everything within the circle, any loan pair electrons and the bonded electrons (the circle breaks any bond in half so just count like 2 instead of 4 if there is a double bond), and subtract that from the number of valence electrons that the atom has.

Julie Park 1G
Posts: 100
Joined: Thu Jul 25, 2019 12:15 am

Re: Shortcut for Formal Charge

Shortcut for formal charge:
# ve- (a neutral atom of the element would have) - (sum of # unpaired electrons + bonds)

Note:
a. count each unpaired electron attached to the atom as a single value
b. count each bond as a single value

For example, say that Nitrogen was surrounded by 1 double bond and 2 unpaired valence electrons. You know that a neutral atom of nitrogen should have 5ve-. Therefore, to find the FC, you would do: 5(ve-) - ( 2 (for each bond in the double bond) + 2 (for each unpaired electron) )
To get 5 - (2+2) or 5-4 which equals 1. The formal charge would be +1
Note: this is just a random theoretical example... not sure if this specific situation is possible

In terms of finding out how you could make the formal charge closer to 0, I guess you could see if it's possible to adjust the number of bonds or unpaired e- relative to the # of valence electrons. For example, since nitrogen has 5ve-, I would try to see if you could change the sum of the # of unpaired e- and bonds so that it equals 5. That way, since 5-5=0, you would get a FC of 0.

selatran1h
Posts: 52
Joined: Fri Aug 30, 2019 12:16 am

Re: Shortcut for Formal Charge

to calculate formal charge, add up the number of electrons surrounding the atom in the lewis structure with the number of bonds attached to it. subtract this value from the number of valence electrons the original atom has to find the formal charge

xenamclean_1G
Posts: 51
Joined: Sat Jul 20, 2019 12:15 am

Re: Shortcut for Formal Charge

What I do to make it faster is subtract the # of electrons for the element in the structure (counting a bond as one) from the valence electrons of that element.

Lizette Noriega 1H
Posts: 105
Joined: Wed Sep 18, 2019 12:15 am

Re: Shortcut for Formal Charge

(# of valence electrons) - (# of electrons + # of bonds) = formal charge

or if you want an even simpler way of thinking about it: (# of valence electrons) - (# of dots + # of lines)

Jenna Ortiguerra 4G
Posts: 50
Joined: Sat Aug 17, 2019 12:18 am

Re: Shortcut for Formal Charge

A shortcut that I use to find formal charge is to find the amount of valence electrons an element has. Then you would draw the Lewis of the compound. To find the formal charge of an element, you would count each bond (essentially each line) as 1, and each lone pair (essentially each dot) as one, then you would add these up. If the amount of valence electrons in the element is the same as the number you counted, the formal charge would be 0. If the amount that you counted os different than the amount of valence electrons of the element, you would subtract the two numbers (# of VE - #of dots and lines).

Jorge Ramirez_4H
Posts: 54
Joined: Wed Nov 21, 2018 12:19 am

Re: Shortcut for Formal Charge

Just count everything around that certain element and if needed subtract the number of initial electrons to the number of lines/dots around the element.

Abigail_Hagen2G
Posts: 107
Joined: Fri Aug 09, 2019 12:17 am

Re: Shortcut for Formal Charge

Just think about the number of lone electrons and the number of lines.

Posts: 52
Joined: Thu Jul 11, 2019 12:16 am

Re: Shortcut for Formal Charge

A quick way to calculate formal charge is to count subtract the sum of the number of lone electrons and bonds by the number of valence electrons.

Posts: 125
Joined: Sat Aug 17, 2019 12:17 am

Re: Shortcut for Formal Charge

AryaG_4C wrote:Does anyone know any short method or trends that make it easier to know/calculate the formal charge of an atom? Like creating a double bond would help the formal charge to be more towards zero etc?

For formal change, a fast way to check (although you should do the calculation (FC = valence - (#bonded e-/2 + e- in lone pair)) is to have the number of valence electrons and subtract the number of dots and number of lines. For example, oxygen with a double bond and two lone pairs is 6 valence electrons minus four dots and two lines, therefore the formal charge is zero. This work because you are taking the valence electrons and indeed subtracting the number of dots (e- in lone pairs) and lines (2 e- per single bond, but you are counting it as one, just like the equation where you divide the number of e- in a covalent bond by 2).

Drake Choi_1I
Posts: 58
Joined: Sat Aug 17, 2019 12:15 am

Re: Shortcut for Formal Charge

I have a shortcut for H O N C. If Hydrogen has 1 bond, oxygen 2, nitrogen 3, carbon 4 then the formal charges will be 0.

AnayaArnold_3L
Posts: 56
Joined: Wed Sep 18, 2019 12:19 am

Re: Shortcut for Formal Charge

a quick shortcut is the just see how many atoms are surrounding whichever molecule you are trying to find the formal charge for and then subtract the valence electrons from that value.

Kaitlynn Tran 3F
Posts: 54
Joined: Wed Sep 18, 2019 12:20 am

Re: Shortcut for Formal Charge

I count each Lewis dot and line around the atom to calculate formal charge. For example, on an oxygen atom that is double bonded to something, there would be 2 lines and 4 valence electrons, resulting in a formal charge of 6.

Akshay Chellappa 1H
Posts: 59
Joined: Wed Sep 11, 2019 12:15 am

Re: Shortcut for Formal Charge

Lyndon showed us that you can draw a circle around one of the atoms and count everything within the circle, any loan pair electrons and the bonded electrons (the circle breaks any bond in half so just count like 2 instead of 4 if there is a double bond), and subtract that from the number of valence electrons that the atom has.

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