## shortcut for FC

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

805098281
Posts: 30
Joined: Thu Sep 27, 2018 11:26 pm

### shortcut for FC

I went to a review session and the TA was getting the FC by counting the electrons or something instead of plugging the numbers into the equation? Does anyone know the shortcut and how it works?

Shash Khemka 1K
Posts: 38
Joined: Thu Sep 27, 2018 11:18 pm

### Re: shortcut for FC

I'm pretty sure the shortcut is [Valence Electrons of the element] - [# of Electrons and Bonds drawn onto that specific element] = FC.

monikac4k
Posts: 44
Joined: Thu Sep 27, 2018 11:25 pm

### Re: shortcut for FC

The long formula for formula charge is:
FC= (valence electrons) - (# lone pair electrons + (# of shared electrons / 2 ) )
The best way I can think of shortening this is by swapping (# of shared electrons / 2 ) with just the number of Lewis lines that signify bonds since each bond line represents 2 electrons. It feels a bit tedious to count the lines, multiply by two to find shared electrons, and then divide by two again for the sake of the formula.
In a way, you can think of formula charge like:
FC= (valence electrons) - (# of lone pair electrons - # of Lewis bonds)

Posts: 47
Joined: Thu Sep 27, 2018 11:23 pm

### Re: shortcut for FC

To find the formal charge, I've just been doing:
Number of valence electrons - the number of atoms directly surrounding the element (wether they are involved in a bond or just a lone pair or a radical)

Esther Ahn 4I
Posts: 30
Joined: Thu Sep 27, 2018 11:29 pm

### Re: shortcut for FC

My TA told me that every bond (line) is counted as one and every lone pair is counted as two. So you would basically just count the number of lines and the number of dots and subtract it from the number of valence electrons!

Rehan Chinoy 1K
Posts: 39
Joined: Thu Sep 27, 2018 11:25 pm

### Re: shortcut for FC

Considering the shortcut would save you approximately 2 seconds for multiplying by 2 and then dividing by 2, I would just stick to how you've been doing it if it's getting you the correct results. :)

Alan Chang
Posts: 33
Joined: Thu Sep 27, 2018 11:29 pm

### Re: shortcut for FC

What I do is I draw a circle around each atom, so you count one electron for each bond and two electrons for each lone pair. Then you just take the valence electrons of the atom and minus it by how much you count.