Formal charge of ions

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Mike Vinci 2B
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Formal charge of ions

Postby Mike Vinci 2B » Thu Dec 07, 2017 12:15 am

Hey guys,
So I thought I heard that in class something like HS04- would have a formal charge of -1 on the central atom. Is this how you confirm you have the right Lewis structure with an ion?

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Re: Formal charge of ions

Postby Chem_Mod » Thu Dec 07, 2017 1:14 am

Not necessarily. The correct Lewis structure would be the one that gives the negative formal charge to the most electronegative atom, which we know typically doesn’t go in the center. In the case of HSO4-, one of the oxygens that has 3 lone pairs and only a single bond to the sulfur would carry the negative formal charge.

Note that this structure also exhibits resonance so in reality, the negative charge is delocalized across the 3 oxygens that aren’t bound to the hydrogen. Regardless, the formal charge isn’t on the central atom like you’d asked in your question.

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