## formal charge and stability

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

Aishwarya Kosgi 1F
Posts: 92
Joined: Wed Sep 30, 2020 10:00 pm

### formal charge and stability

Hi! I had a question about formal charge and rewriting structures. I think Dr. Lavelle mentioned that if a structure can be redrawn so the atoms in the compound have a formal charge of 0, that means the compound is more stable? Would we check every time one of the atoms has a formal charge that is not 0 to see if we can redraw the structure? And also would someone be able to explain how the compound is more stable in terms of the location of the electrons? Thanks!

Sydney Lam_2I
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Joined: Wed Sep 30, 2020 10:09 pm

### Re: formal charge and stability

Hi!

So I asked my TA this question too! She said that every time we draw a lewis structure, we need to check for formal charge in order to draw the best structure. Also, we would want the formal charge of each atom in the structure to be zero ideally. If not, we would want to be as close as possible! I don't quite understand what you mean by the structure being stable based on where the electron is though so, if you could elaborate more maybe I could help you!

Emily Vu 1L
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### Re: formal charge and stability

hi!

so a good starting point for when you're drawing structures, is to 1) make sure your drawing is symmetrical (for example, H2O should be drawn H - O - H) and to 2) use double bonds if the atom can accommodate an expanded octet, which Dr. Lavelle mentioned, is if the atom is in the p-block of period 3 or later in the periodic table. and yes, you should always try to make the formal charge as close to zero as possible BUT if the atom is charged (i.e. it is a cation/anion), then the formal charges should add up to the total charge. and if I understand correctly about your last question, in terms of the location of electrons, an atom tries to space its elements in the most symmetrical manner as possible in order to reduce electron-electron repulsion. I believe we will discuss that more in detail when we talk about geometric shape (in a couple weeks Dr. Lavelle said) which discusses VSEPR theory. hope this helps!

Leyla Anwar 3B
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Joined: Wed Sep 30, 2020 10:03 pm

### Re: formal charge and stability

If you can't get the total charge to 0 (FC=0 for all atoms) then would you want any specific atom to be the one that can get FC=0 (if possible at all)? Like, would it be the atom in the center of the lewis structure? Or the atom with the highest or lowest electronegativity?

Jack_Pearce_2H
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Joined: Wed Sep 30, 2020 9:48 pm

### Re: formal charge and stability

Try to get it as close as possible to 0! The closer it is the more stable, but if you really cannot get it to 0 thats okay too :)

Carly_Lipschitz_3H
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Joined: Wed Sep 30, 2020 9:56 pm

### Re: formal charge and stability

This is a good question. I know it's best to get formal charges of 0 to make it most stable. But how do we know when to stop manipulating the Lewis Structure? How do we know when we are close enough to the most stable form?

Crystal Pan 2G
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### Re: formal charge and stability

It is of course best for the whole structure to have a formal charge of 0, but if that doesn't happen, i think the second most stable form is when the central atom has a formal charge of 0.

Izamary Marquez 2H
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Joined: Wed Sep 30, 2020 9:44 pm

### Re: formal charge and stability

Crystal Pan 1B wrote:It is of course best for the whole structure to have a formal charge of 0, but if that doesn't happen, i think the second most stable form is when the central atom has a formal charge of 0.

As you make the charges of the outer electrons zero, wouldn't this start to make the central atom's charge also zero? Lavelle seems to automatically know how the charges cancel out..

Sabrina Galvan 3J
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### Re: formal charge and stability

Carly_Lipschitz_3L wrote:This is a good question. I know it's best to get formal charges of 0 to make it most stable. But how do we know when to stop manipulating the Lewis Structure? How do we know when we are close enough to the most stable form?

We know we're close to the most stable form when the most electronegative ions carry the negative charges and the structure has the smallest magnitude of charges.