shortcut for FC


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805098281
Posts: 30
Joined: Fri Sep 28, 2018 12:26 am

shortcut for FC

Postby 805098281 » Fri Nov 02, 2018 6:08 pm

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: Fri Sep 28, 2018 12:18 am

Re: shortcut for FC

Postby Shash Khemka 1K » Fri Nov 02, 2018 6:35 pm

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

monikac4k
Posts: 56
Joined: Fri Sep 28, 2018 12:25 am

Re: shortcut for FC

Postby monikac4k » Fri Nov 02, 2018 7:10 pm

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)

Madeline Motamedi 4I
Posts: 62
Joined: Fri Sep 28, 2018 12:23 am

Re: shortcut for FC

Postby Madeline Motamedi 4I » Sat Nov 03, 2018 11:46 pm

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: Fri Sep 28, 2018 12:29 am

Re: shortcut for FC

Postby Esther Ahn 4I » Sun Nov 04, 2018 1:31 am

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: 67
Joined: Fri Sep 28, 2018 12:25 am

Re: shortcut for FC

Postby Rehan Chinoy 1K » Sun Nov 04, 2018 9:42 am

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: Fri Sep 28, 2018 12:29 am

Re: shortcut for FC

Postby Alan Chang » Sun Nov 04, 2018 1:52 pm

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.


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