most stable structure
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most stable structure
Professor said that the most stable formal charge is 0. So when he showed the two structure examples of SO4^2- during the lecture, how did he know the second structure (the one where sulfur had two double bonds) was the most stable?
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Re: most stable structure
To find formal charge you use the formula FC=V-[L+(S/2)] where FC=formal charge, V=valence electrons in the ground state atom, L=lone pair electrons and S=shared electrons.
You then use this formula for each atom and edit your Lewis structure to have the most atoms with a formal charge of 0.
With the SO4^2- example the second double bond caused one oxygen formal charge and the sulfur formal charge to change to 0 because the equation changed for those atoms making the ion more stable than if it had one double bond.
You then use this formula for each atom and edit your Lewis structure to have the most atoms with a formal charge of 0.
With the SO4^2- example the second double bond caused one oxygen formal charge and the sulfur formal charge to change to 0 because the equation changed for those atoms making the ion more stable than if it had one double bond.
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Re: most stable structure
Also, when looking at the two Lewis structures that Professor Lavelle drew, we can see that the first structure has the central sulfur atom with a formal charge of +2, meaning that the positive charge will pull the electrons from the oxygen atoms (with -1 charges) in, resulting in a less stable structure. On the other hand, the second structure has a central sulfur atom with a formal charge of 0, which won't cause a strong pull on the electrons from the oxygen atoms, resulting in a more stable and desirable structure.
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Re: most stable structure
He found it by calculating the formal charge for each atom, using the formula FC = V - (L+(s/2)). When there is a large difference between the formal charges of each atoms, it is more likely to be unstable because the positive ones pull the negative ones towards it, whereas when the charges are both 0, it is more stable.
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Re: most stable structure
He was able to see that the sulfur in the structure with 2 double bonds was more stable by looking at the individual formal charges of each atom. In the structure with only single bonds the formal charges are:
Oxygen: FC = V - (L +S/2) = 6 - (6 + 2/2) = -1
Sulfur: FC = 6 - (0 + 8/2) = +2
FC of all atoms have to add up to overall charge: 4 x (-1) + 2 = -2
In the structure with 2 double bonds, the formal charges of the 2 oxygens double bonded to sulfur and the sulfur atom are:
Oxygen: FC = 6 - (4 + 4/2) = 0
Sulfur: FC = 6 - (0 + 12/2) = 0
Because the formal charges of three of the five atoms in the molecule can be brought to 0, it is more stable.
Oxygen: FC = V - (L +S/2) = 6 - (6 + 2/2) = -1
Sulfur: FC = 6 - (0 + 8/2) = +2
FC of all atoms have to add up to overall charge: 4 x (-1) + 2 = -2
In the structure with 2 double bonds, the formal charges of the 2 oxygens double bonded to sulfur and the sulfur atom are:
Oxygen: FC = 6 - (4 + 4/2) = 0
Sulfur: FC = 6 - (0 + 12/2) = 0
Because the formal charges of three of the five atoms in the molecule can be brought to 0, it is more stable.
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Re: most stable structure
Hi! The way I think about it is that there is "net" formal charge and formal charge. Net formal charge refers to the formal charge of the structure in general and formal charge can be designated to individual atoms in the molecule. For instance, the net formal charge of both SO4^2- is 0 but the one with two double bonds is the most stable because there are no individual formal charges for atoms whereas the entirely single bonded structure had formal charges that canceled out in the net formal charge.
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Re: most stable structure
Dr. Lavelle was able to come to the conclusion that the sulfur with the structure of the double bond was more stable through finding the formal charge on the sulfur atom in the compound. Overall, if an atom has a formal charge of 0, it is most stable. The lower the formal charge, the more stable the structure becomes.
FC = V - (L + S/2)
Single Bond:
O: 6 - (6 + 2/2) = -1
S: 6 - (0 + 8/2) = +2
Double Bond:
O: 6 - (4 + 4/2) = 0
S: 6 - (0 + 12/2) = 0
FC = V - (L + S/2)
Single Bond:
O: 6 - (6 + 2/2) = -1
S: 6 - (0 + 8/2) = +2
Double Bond:
O: 6 - (4 + 4/2) = 0
S: 6 - (0 + 12/2) = 0
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