Which atom to have the charge in lewis structures

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Megan Potter 1G
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Joined: Fri Apr 06, 2018 11:04 am

Which atom to have the charge in lewis structures

Postby Megan Potter 1G » Tue May 15, 2018 9:04 pm

So in a UA session, we learned when you are writing the Lewis structure for a molecule that has a charge, the most electronegative atom should carry the negative charge. for example, in OCN-, Oxygen is the most electronegative. When drawing the structure, one of the atoms needs to have a -1 to make the entire molecule -1 so the formal charges for C and N should be 0 and the formal charge for oxygen should be -1, giving the entire molecule a negative charge.

my question is if a molecule has a positive charge, should the positive charge go on the LEAST electronegative atom or still the most?

nicolesalcedo
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Joined: Fri Apr 06, 2018 11:05 am

Re: Which atom to have the charge in lewis structures

Postby nicolesalcedo » Tue May 15, 2018 11:02 pm

I believe that the charge should be on whatever atom has the extra/remaining (whether it be positive or negative) charge.
For example, during lecture on Friday, one of the TA's wrote the lewis structure of SO4-2 with 4 single bonds (all the O's had -1 charge and the S had a +2 charge). After rewriting the structure with two double bonds and 1 single bond, the -1 charges were left on the two O's connected with the single bonds (the S and the other two O's with double bonds were not written with a charge).
You can think of it as canceling out the negative and positive charges of the whole structure. Hope this makes sense?

Chem_Mod
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Re: Which atom to have the charge in lewis structures

Postby Chem_Mod » Wed May 16, 2018 12:05 pm

Yes, the positive formal charge is more stable on the least electronegative element.
However, this rule is not as important as the octet rule for C, N, O, F, Ne.


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