Chemical Forums

Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: PopcornMuffin on December 05, 2007, 12:32:18 AM

Title: HClO4 Best Resonance Structure
Post by: PopcornMuffin on December 05, 2007, 12:32:18 AM

I'm trying to find the resonance structure of HClO4 that contributes most to its true structure.

All four O atoms are bonded to the central chlorine atom and the H atom is bonded to an oxygen atom.
Cl will have a formal charge of zero and an expanded octet.

I can't figure out a way to draw this out. With an expanded octet, I keep giving Cl a formal charge of either +1 or +2.

Title: Re: HClO4 Best Resonance Structure
Post by: AWK on December 05, 2007, 01:27:31 AM

What do you mean by an expanded octet.
In the case of HCLO4 forget octet rule.
Draw a tentative structure with three doble bonds. Then split the second bond of each double bond separately to form 3 resonance structure with a formal charge +1 on Cl.
Going by the same way split 2 of double bonds. You will gett next three resonance structure with +2 charge on Cl atom.
Finally do the same with all double bond. This will give you one resonance structure with +3 formal charge at Cl.

Title: Re: HClO4 Best Resonance Structure
Post by: agrobert on December 05, 2007, 03:35:19 PM

Chlorine has a +7 oxidation state in HClO₄.

http://en.wikipedia.org/wiki/Perchlorate

Title: Re: HClO4 Best Resonance Structure
Post by: AWK on December 06, 2007, 12:59:19 AM

Quote from: agrobert on December 05, 2007, 03:35:19 PM

Chlorine has a +7 oxidation state in HClO₄.

http://en.wikipedia.org/wiki/Perchlorate

This is a trivial statement in this discussion.
We discuss here about formal charge of Cl in different resonance structure, not about oxidation number oc chlorine.
A mean structure of chlorate(VII) anion is mean and idealized one and does not give any information on number of possible resonance forms, except that they exists. In my crystallographic experience I did not found such idealized form of chlorate.