Recognizing lowest formal charge

Moderators: Chem_Mod, Chem_Admin

Connie Liang 3L
Posts: 59
Joined: Wed Sep 30, 2020 10:00 pm
Been upvoted: 1 time

Recognizing lowest formal charge

Postby Connie Liang 3L » Fri Nov 13, 2020 7:39 pm

Are there any ways to make sure you're always drawing the lowest formal charge? For example, after drawing a Lewis Structure are we supposed to calculate using the formal charge formula the charge of each atom, or are there general tips to know to make sure you're always drawing structures with lowest formal charge?

DominicMalilay 1F
Posts: 114
Joined: Wed Sep 30, 2020 9:36 pm

Re: Recognizing lowest formal charge

Postby DominicMalilay 1F » Fri Nov 13, 2020 7:43 pm

I think the general tip is that the more symmetrical the lewis structure is, it will probably be the lowest formal charge. Of course, you can check each structures' formal charges and the one with the most formal charges of 0 would be the lowest.

Eliana Witham 2H
Posts: 101
Joined: Wed Sep 30, 2020 9:48 pm
Been upvoted: 2 times

Re: Recognizing lowest formal charge

Postby Eliana Witham 2H » Fri Nov 13, 2020 8:06 pm

I like to draw the lewis structure and make sure the electron count is correct first. Then, I'll find the formal charges and draw a new lewis structure if it lowers the formal charges. Hope that helps a little!

Olivia Monroy 1A
Posts: 103
Joined: Wed Sep 30, 2020 10:00 pm

Re: Recognizing lowest formal charge

Postby Olivia Monroy 1A » Fri Nov 13, 2020 8:06 pm

If there is uncertainty because there are resonance structures I usually check formal charge after drawing the Lewis structure, but yeah as said also drawing a symmetric structure is a good approach. If you have any uncertainty just use the FC equation to double check. The resonance structure with the least number of formal charges is most stable, and the most electronegative atoms will have negative charge least electronegative positive charge.

Crystal Pan 2G
Posts: 118
Joined: Wed Sep 30, 2020 10:04 pm
Been upvoted: 2 times

Re: Recognizing lowest formal charge

Postby Crystal Pan 2G » Fri Nov 13, 2020 9:07 pm

calculate the number of electrons, then find the atom with lowest ionization energy to put in the center, then find the number of lone pairs on the central atom and how many bonds the central atom forms, and then you draw the structure out with as much symmetry as possible. Then you can calculate the FC for each atom to make sure that you are drawing the most stable structure possible.

Victoria Dao 3G
Posts: 99
Joined: Wed Sep 30, 2020 9:50 pm

Re: Recognizing lowest formal charge

Postby Victoria Dao 3G » Fri Nov 13, 2020 9:36 pm

Unfortunately, I think for this we do have to calculate the formal charge after drawing each lewis structure. For me at least, this is the only way to verify which structure has the most 0 formal charges on atoms.

Eric Cruz 2G
Posts: 92
Joined: Wed Sep 30, 2020 9:45 pm
Been upvoted: 1 time

Re: Recognizing lowest formal charge

Postby Eric Cruz 2G » Sat Nov 14, 2020 12:23 am

For the most part, it is best to draw the first lewis dot structure that is possible. Then once you have the "standard" lewis structure, try to see if you can create other lewis structures that still satisfy the octet rule and the needed total electrons. Generally, the best way to get the lowest formal charge is creating double bonds. For example when oxygen is double bonded with another element, its formal charge is 0 and a formal charge of 0 is the most ideal.

Sabrina Galvan 3J
Posts: 96
Joined: Wed Sep 30, 2020 9:35 pm
Been upvoted: 1 time

Re: Recognizing lowest formal charge

Postby Sabrina Galvan 3J » Sat Nov 14, 2020 7:36 pm

To draw a Lewis strucutre with the lowest formal charge, the first step is have the central atom be the one with the lowest ionization energy, then when calculating the formal charges, the negative charges should be on the most electronegative atoms. It should also have the fewest and smallest magnitude of formal charges.

Mackenzie Stockton 2H
Posts: 102
Joined: Wed Sep 30, 2020 10:11 pm

Re: Recognizing lowest formal charge

Postby Mackenzie Stockton 2H » Sat Nov 14, 2020 9:10 pm

I dont think there is any set rule, but I like to draw the lewis structure with the lowest formal charge that I can think of and then quickly draw some other options just to make sure that it does in fact have the lowest possible formal charge. Helpful tips would be to make sure that the most electronegative atom has the negative formal charge (if there is a - FC in the diagram), as this is the most stable structure.

Chinyere Okeke 2J
Posts: 98
Joined: Wed Sep 30, 2020 10:05 pm
Been upvoted: 1 time

Re: Recognizing lowest formal charge

Postby Chinyere Okeke 2J » Sat Nov 14, 2020 9:16 pm

To draw the Lewis Structure with the lowest charge on each atom (so basically the most stable structure) an LA mentioned a tip: when the molecule has a net charge that is negative, you give the most electronegative element the charge.

So for NCO- you would assign the O the -1 formal charge. And that will give you the most stable structure.

And for a molecule with a net charge that is positive, you would assign the least electronegative element the charge.

Connie Liang 3L
Posts: 59
Joined: Wed Sep 30, 2020 10:00 pm
Been upvoted: 1 time

Re: Recognizing lowest formal charge

Postby Connie Liang 3L » Sun Nov 15, 2020 8:17 pm

Chinyere Okeke 2A wrote:To draw the Lewis Structure with the lowest charge on each atom (so basically the most stable structure) an LA mentioned a tip: when the molecule has a net charge that is negative, you give the most electronegative element the charge.

So for NCO- you would assign the O the -1 formal charge. And that will give you the most stable structure.

And for a molecule with a net charge that is positive, you would assign the least electronegative element the charge.

Thank you Chinyere for relaying that! That's super helpful :)

Jerry_T
Posts: 94
Joined: Wed Sep 30, 2020 9:46 pm

Re: Recognizing lowest formal charge

Postby Jerry_T » Sun Nov 15, 2020 11:04 pm

There's no way to recognize the formal charge without calculating so I draw Lewis structures by counting the number of electrons, then trying different bonds for the lowest formal charge.


Return to “Lewis Structures”

Who is online

Users browsing this forum: No registered users and 1 guest