Checking bonding


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Jedrick Zablan 3L
Posts: 68
Joined: Sat Aug 17, 2019 12:17 am

Checking bonding

Postby Jedrick Zablan 3L » Sat Oct 26, 2019 2:17 pm

Is checking the formal charge the only way to make sure your lewis structure is correct? Or is there another method?

AnnikaMittelhauser4E
Posts: 50
Joined: Fri Aug 30, 2019 12:18 am

Re: Checking bonding

Postby AnnikaMittelhauser4E » Sat Oct 26, 2019 2:30 pm

I don't think so since even checking formal charge I don't think can tell you if you're correct - it can just tell you which potential lewis structures are better/more likely to be correct. But, when it comes to figuring out a good lewis structure that is likely to be experimentally correct, you can look at a few things..

1. It has the correct number of electrons (add up valence electrons of component elements and add/subtract for anion/cation).
2. Ideally the component atoms all have formal charges of 0 unless the molecule is charged (in which case the FCs need to add up to the overall charge)
- but if impossible, there are less elements with formal charges (and those charges are smaller magnitude) *and* the negative FCs are on the more electronegative elements.
3. No n=1 or n=2 elements have an expanded octet.
4. Oxygen and carbon have an octet for sure.
5. Hydrogen has two electrons instead of an octet.
6. If it could have resonance, it probably does, since that makes molecules more stable.

Michelle Shin 4B
Posts: 50
Joined: Thu Jul 25, 2019 12:17 am

Re: Checking bonding

Postby Michelle Shin 4B » Sat Oct 26, 2019 2:58 pm

Comparing the formal charges of atoms in Lewis structures helps you find which is the more stable structure, but I'm not sure if this is the only method to see which is the best structure.

KTran 1I
Posts: 52
Joined: Fri Aug 30, 2019 12:15 am

Re: Checking bonding

Postby KTran 1I » Sun Oct 27, 2019 12:50 pm

AnnikaMittelhauser4E wrote:I don't think so since even checking formal charge I don't think can tell you if you're correct - it can just tell you which potential lewis structures are better/more likely to be correct. But, when it comes to figuring out a good lewis structure that is likely to be experimentally correct, you can look at a few things..

1. It has the correct number of electrons (add up valence electrons of component elements and add/subtract for anion/cation).
2. Ideally the component atoms all have formal charges of 0 unless the molecule is charged (in which case the FCs need to add up to the overall charge)
- but if impossible, there are less elements with formal charges (and those charges are smaller magnitude) *and* the negative FCs are on the more electronegative elements.
3. No n=1 or n=2 elements have an expanded octet.
4. Oxygen and carbon have an octet for sure.
5. Hydrogen has two electrons instead of an octet.
6. If it could have resonance, it probably does, since that makes molecules more stable.

This is great comprehensive list of some of the ways to check to see if your Lewis structure is correct, but I also wanted to add that it is helpful to remember that H will want to form one bond, oxygen will want to form two bonds, nitrogen will want to form three, and carbon will tend to form four. This may be helpful in checking whether or not double or triple bonds are needed.


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