Formal Charge on each atom


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904571591
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Joined: Fri Sep 25, 2015 3:00 am

Formal Charge on each atom

Postby 904571591 » Sun Jul 23, 2017 10:21 pm

Hi,
Is there any easier way to know the formal charge on each atom? except using the formula.

Chem_Mod
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Re: Formal Charge on each atom

Postby Chem_Mod » Sun Jul 23, 2017 10:26 pm

You can try to learn some patterns for commonly seen atoms so you don't always have to calculate their formal charge using the formula.

For instance, oxygen with 2 bonds and 2 lone pairs has zero formal charge. With one more bond (3 bonds, 1 lone pair), it has a +1 charge. With 1 less bond (1 bond, 3 lone pairs), it has a -1 charge.

There is a similar pattern for nitrogen:
- neutral: 3 bonds, 1 lone pair
- one more bond than neutral (4 bonds, 0 lone pairs): +1 charge
- one less bond than neutral (2 bonds, 2 lone pairs): -1 charge

504754253
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Re: Formal Charge on each atom

Postby 504754253 » Sun Jul 23, 2017 10:56 pm

valence electron - (# of bonds + # of lone pairs)

Michelle Steinberg2J
Posts: 73
Joined: Fri Sep 29, 2017 7:04 am

Re: Formal Charge on each atom

Postby Michelle Steinberg2J » Tue Oct 31, 2017 9:03 pm

I think the most safe way to determine formal charge is using the formula Lavelle showed us in lecture:
Formal Charge=Valence-(Lone+shared/2)

But, I did learn a different way in my high school chem class that I've been using. Basically, you just look at the periodic table and look at how many valence electrons an element SHOULD have. So, for example, Sulfur should have 6 valence electrons. If your drawing has 5, it needs one more valence electron added, therefore the formal charge is +1. If your drawing has 6, it does not need any more, so the formal charge is 0. If it has 7, it needs one less, so the formal charge is -1.

Too many = -(extra electrons)
Too little = +(needed electrons)

Peri Bingham 1G
Posts: 50
Joined: Fri Sep 29, 2017 7:03 am

Re: Formal Charge on each atom

Postby Peri Bingham 1G » Mon Nov 13, 2017 10:48 pm

An easier way to determine formal charge is to count each dot (electron) as 1 and each bond as 1. Add up the number of dots and bonds on an atom and subtract that from the atom's number of valence electrons. That will determine the formal charge of the atom.


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