From chemistry-request@ccl.net Mon Jun 2 17:45:42 2003 Received: from mx3.trentu.ca (mx3.trentu.ca [192.75.12.4]) by server.ccl.net (8.12.8/8.12.8) with SMTP id h52LjggC011365 for ; Mon, 2 Jun 2003 17:45:42 -0400 Received: (qmail 31253 invoked by uid 504); 2 Jun 2003 21:45:42 -0000 Received: from elewars/at/trentu.ca by mx3.trentu.ca by uid 501 with qmail-scanner-1.14 (fsecure: 4.15/4370/2003-05-30/2003-05-30. 2003-05-27/ Clear:. Processed in 0.321447 secs); 02 Jun 2003 21:45:42 -0000 X-Qmail-Scanner-Mail-From: elewars/at/trentu.ca via mx3.trentu.ca X-Qmail-Scanner: 1.14 (Clear:. Processed in 0.321447 secs) Received: from unknown (HELO trentu.ca) (209.42.101.30) by mx3.trentu.ca with SMTP; 2 Jun 2003 21:45:41 -0000 Message-ID: <3EDBC646.604C269A/at/trentu.ca> Date: Mon, 02 Jun 2003 17:48:54 -0400 From: elewars X-Mailer: Mozilla 4.79 [en] (WinNT; U) X-Accept-Language: en MIME-Version: 1.0 To: "Shobe, Dave" , chemistry/at/ccl.net Subject: Re: CCL:hybrid/VSEPR References: <5CF08BBFE6DE97478C1E76E654CAF90801BC0C05/at/lvlxch02.ntdomain.americas.sc-world.com> Content-Type: multipart/alternative; boundary="------------DE2EBAAB135F692D3721CACB" --------------DE2EBAAB135F692D3721CACB Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit 2003 June 2 Hello, re hybridization vs. VSEPR: Hybridization is purely a mathematical procedure, whereby electron density is resolved into components, rather than a physically real phenomenon that occurs before bonding. It "...is _never_ necessary" (J. Simons and J. Nichols, "Quantum Mechanics in Chemistry", Oxford U Press, New York, 1997, p. 133). I view it as being analogous to resolving a force into components, and indeed, like forces, orbitals are mathematically vectors (in Hilbert space); so it legitimate to take linear combinations of them. The VSEPR model, on the other hand, seems to me to be an attempt to provide a _physical_ explanation of the shape of molecules, namely electrostatic repulsion. Actually, I suspect that Pauling (a popularizer, if indeed not the originator of the concept) thought of hybridization as "real", and staunchly championed the bent bonds model of the C/C double bond over the sigma/pi view. (About 5 years ago someone posted an amusing anecdote about Pauling to the CCL: asked if orbitals are real, he is supposed to have said "They must be real, because Mulliken and I have been using them for the past [30 or whatever] years".) E. Lewars ==== "Shobe, Dave" wrote: > > > That's an interesting observation. > > Structures of main-group (including organic) compounds are often > rationalized in terms of hybridization, which because it relies on > orbitals implies a small role for interelectron repulsion. > > However, these same structures are often rationalized using VSEPR > theory, which is 100% based on interelectron repulsion, at least if > you ignore the underlying assumption that electrons, for mysterious > reasons, come in pairs. > > --David Shobe > S|d-Chemie Inc. > phone (502) 634-7409 > fax (502) 634-7724 > email dshobe/at/sud-chemieinc.com > > Don't bother flaming me: I'm behind a firewall. > > > -----Original Message----- > From: Avijit Ghosh [mailto:avijit/at/physics.drexel.edu] > Sent: Friday, May 30, 2003 7:01 PM > To: chemistry/at/ccl.net > Subject: CCL:Orbitals > > ....... > > > (2) Does the single e- wavefunction density have any > > meaning? Let me decompose this a bit. To me the fact that > > organic chemists can "hybridize" orbitals (aka "handwaving > > quantum mechanics") is a testament to the contribution of > > e-e- correlation as actually not being that much at least > > for the first part of the periodic table. In fact that elements > have > > the properties that they do is also a testament to this. > > ....... --------------DE2EBAAB135F692D3721CACB Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit 2003 June 2

Hello, re hybridization vs. VSEPR:

Hybridization is purely a mathematical procedure, whereby electron density is resolved into components, rather than a physically real phenomenon that occurs before bonding. It "...is _never_  necessary" (J. Simons and J. Nichols, "Quantum Mechanics in Chemistry", Oxford U Press, New York, 1997, p. 133). I view it as being analogous to resolving a force into components, and indeed, like forces, orbitals are mathematically vectors (in Hilbert space); so it legitimate to take linear combinations of them. The VSEPR model, on the other hand, seems to me to be an attempt to provide a _physical_ explanation of the shape of molecules, namely electrostatic repulsion.

Actually, I suspect that Pauling (a popularizer, if indeed not the originator of the concept) thought of hybridization as "real", and staunchly championed the bent bonds model of the C/C double bond over the sigma/pi view. (About 5 years ago someone posted an amusing anecdote about Pauling to the CCL: asked if orbitals are real, he is supposed to have said "They must be real, because Mulliken and I have been using them for the past [30 or whatever] years".)

E. Lewars
====

"Shobe, Dave" wrote:

 

That's an interesting observation.

Structures of main-group (including organic) compounds are often rationalized in terms of hybridization, which because it relies on orbitals implies a small role for interelectron repulsion.

However, these same structures are often rationalized using VSEPR theory, which is 100% based on interelectron repulsion, at least if you ignore the underlying assumption that electrons, for mysterious reasons, come in pairs.

--David Shobe
Süd-Chemie Inc.
phone (502) 634-7409
fax     (502) 634-7724
email  dshobe/at/sud-chemieinc.com

Don't bother flaming me: I'm behind a firewall.
 

-----Original Message-----
From: Avijit Ghosh [mailto:avijit/at/physics.drexel.edu]
Sent: Friday, May 30, 2003 7:01 PM
To: chemistry/at/ccl.net
Subject: CCL:Orbitals

.......

>       (2) Does the single e- wavefunction density have any
> meaning? Let me decompose this a bit. To me the fact that
> organic chemists can "hybridize" orbitals (aka "handwaving
> quantum mechanics") is a testament to the contribution of
> e-e- correlation as actually not being that much at least
> for the first part of the periodic table. In fact that  elements have
> the properties that they do is also a testament to this.

.......

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