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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: kimyacı on December 19, 2009, 09:42:05 AM

Title: Ozone
Post by: kimyacı on December 19, 2009, 09:42:05 AM
 Hello all
I wonder about why ozone is not triangular, it is angular.
Thanks in advance...
Title: Re: Ozone
Post by: Schrödinger on December 19, 2009, 11:39:38 AM
Think on the following lines
How exactly does a molecule look like?
Would you consider electron pair structure or molecular structure?
Title: Re: Ozone
Post by: 408 on December 19, 2009, 01:03:49 PM
Think of the bond strain!  On an oxygen-oxygen bond  :o
Title: Re: Ozone
Post by: Schrödinger on December 19, 2009, 01:04:58 PM
What bond strain on an oxygen-oxygen bond?
Title: Re: Ozone
Post by: Grundalizer on December 19, 2009, 10:07:19 PM
(http://upload.wikimedia.org/wikipedia/commons/thumb/a/a6/Ozone-1%2C3-dipole.png/800px-Ozone-1%2C3-dipole.png)

Sure, you could make a triangle out of it.  Draw a line connecting the bottom two Oxygens, and you have one angle of 116.8, and two others of 31.6 degrees.  It just so happens that chemists decided to call a molecule that has a molecular geometry with 3 atoms that has a bond angle of about 120 degrees Bent(angular).

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

Why do we call a rock a rock and not a hamster?  Just the name people chose a long time ago.



Title: Re: Ozone
Post by: 408 on December 19, 2009, 10:11:34 PM
The bond strain on the theoretical triangular ozone molecule.  O-O single bonds even when unstrained are not exactly stable.  Think organic peroxides...
Try forcing the 116.8 degree angle in the bent ozone molecule to the 60 required for a triangular molecule...
Title: Re: Ozone
Post by: Schrödinger on December 19, 2009, 11:05:20 PM
Try forcing the 116.8 degree angle in the bent ozone molecule to the 60 required for a triangular molecule...

Why is 60o required for triangular molecule?
Why do you need to force the 116.8 degree angle?
The bond angle has to be 120 for a trigonal planar molecule.
Consider BF3 , SO3 , etc.. Their bond angles are 120, not 60.
See http://en.wikipedia.org/wiki/Trigonal_planar_molecular_geometry


About the bond strain.... The O-O bond length is between that of a single bond and a double bond due to resonance. So, isn't it sort of stronger than the O-O single bond of the peroxide?


Title: Re: Ozone
Post by: Grundalizer on December 19, 2009, 11:26:27 PM
Quote
Why is 60o required for triangular molecule?
Why do you need to force the 116.8 degree angle?
The bond angle has to be 120 for a trigonal planar molecule.
Consider BF3 , SO3 , etc.. Their bond angles are 120, not 60.

I agree
Title: Re: Ozone
Post by: 408 on December 20, 2009, 12:14:04 AM
*Facepalm*

We are thinking two different things...

The original poster wondered why ozone was not 'triangular'. I took this to mean a ring of 3 oxygens singly bonded in a triangular ring, especially as the original poster said ozone is actually angular; which I assumed to be a bad term for a 'bent' molecule.  'Triangular' or 'cyclic' is obviously not the structure of ozone; That is of course as you described; the bent form, which the original poster called 'angular'.  My explanations were for why this cyclic containing 3 oxygens in a ring could not exist.  I never once said ozone actually adopts this cyclic, triangular form, I used the original poster's own terminology in the hopes that he would understand, without having to introduce extra jargon to confuse

*Facepalm*

Way to go...
Title: Re: Ozone
Post by: sjb on December 20, 2009, 05:00:15 AM
Just to murky the waters still further, why do both cyclopropane and propene exist? One has the triangle structure (which I too read as being an equilateral triangle), and the other the single/double bond complex?
Title: Re: Ozone
Post by: BluRay on December 20, 2009, 09:18:54 AM
Just to murky the waters still further, why do both cyclopropane and propene exist? One has the triangle structure (which I too read as being an equilateral triangle), and the other the single/double bond complex?
Probably because of the same reason you can have both diamond and graphite: in the right conditions, a chemical can assume more than one form, because it has more than one local minimum of gibbs energy.
Title: Re: Ozone
Post by: Markovnikov on December 21, 2009, 01:05:33 PM
Just to murky the waters still further, why do both cyclopropane and propene exist? One has the triangle structure (which I too read as being an equilateral triangle), and the other the single/double bond complex?
Probably because of the same reason you can have both diamond and graphite: in the right conditions, a chemical can assume more than one form, because it has more than one local minimum of gibbs energy.

Please note the difference between an allotrope and an isomer.

To answer the first poster:

PMO theory.
The MO diagram for ozone for a triangular ozone D3h would invoke a second-order Jahn-Teller degeneracy and force the structure to decrease the symmetry towards a less symmetrical structure, the bent structure.
Title: Re: Ozone
Post by: Schrödinger on December 21, 2009, 01:07:34 PM
What's PMO theory?

Could you give me a brief intro? Cuz all websites offer long-winding explanations.
Title: Re: Ozone
Post by: Markovnikov on December 21, 2009, 01:10:57 PM
Perturbation Molecular Orbital Theory.
Read more here:
http://www.chm.davidson.edu/vce/MolecularOrbitals/index.html

Title: Re: Ozone
Post by: Schrödinger on December 21, 2009, 01:13:05 PM
Perturbation Molecular Orbital Theory.
Read more here:
http://www.chm.davidson.edu/vce/MolecularOrbitals/index.html


That's just MO theory. How is PMO different from it?
Title: Re: Ozone
Post by: Markovnikov on December 21, 2009, 01:22:14 PM
Instead of calculations which you do with regular MO theory, PMO uses qualitative reasoning between the interacting orbitals.

The link probably isn't a good one at all. But couldn't really find any good ones from .edu  :-[
Title: Re: Ozone
Post by: Mitch on December 21, 2009, 02:40:35 PM
So qualitative MO is simply called PMO?
Title: Re: Ozone
Post by: Markovnikov on December 21, 2009, 03:15:18 PM
Well, I'm sure there's something more to it than a qualitative part...

But from my course, it's called PMO...
Title: Re: Ozone
Post by: BluRay on December 22, 2009, 07:58:54 AM
Just to murky the waters still further, why do both cyclopropane and propene exist? One has the triangle structure (which I too read as being an equilateral triangle), and the other the single/double bond complex?
Probably because of the same reason you can have both diamond and graphite: in the right conditions, a chemical can assume more than one form, because it has more than one local minimum of gibbs energy.

Please note the difference between an allotrope and an isomer.
Yes, but the principle is the same.