Formal Charge on Central Atom

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Wesley Shen Lec 4
Posts: 23
Joined: Fri Sep 25, 2015 3:00 am

Formal Charge on Central Atom

Postby Wesley Shen Lec 4 » Mon Oct 19, 2015 8:37 pm

So on Chapter 3 Problem 57. c., it asks us to draw out possible Lewis Structures for the perchlorate ion, CLO4-.
The answer the solutions manual gives is it's a resonance structure with 3 triple bonds between Cl and O and one single bond between Cl and the remaining O, because this gives us a formal charge of 0 for Cl, and 0 for 3 O atoms and -1 for one O atom.
However, if we draw it so that Cl is double bonded to all 4 O atoms (which is possible following the rules, right?), this would yield a formal charge of -1 on Cl and 0 on all 4 O atoms.
So my question is, why can't the Lewis Structure be all 4 O atoms double bonded to Cl? It yields the same number of atoms with a 0 formal charge. Is it because Cl is more electronegative than O, so it would have -1? Or does it have to do with the formal charge of the central atom being more important?

Ronald Yang 2F
Posts: 86
Joined: Fri Sep 25, 2015 3:00 am

Re: Formal Charge on Central Atom

Postby Ronald Yang 2F » Mon Oct 19, 2015 9:38 pm

I think you meant 3 "double" bonds, but, the reason why oxygen with the -1 is the solution is because oxygen is more electronegative than chlorine. Chlorine is not as electronegative, even though it is to the right of oxygen (it still is a row below). Putting a formal charge of -1 on chlorine is not as favorable as putting a formal charge of -1 on oxygen due to oxygen's comparably higher electronegativity. By convention, you would want to put the negative formal charge on the most electronegative element, as this element would be the most likely to want that electron for its own and like having that negative charge.

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