Subject: CCL:orbitals and reality

From: "Jens Spanget-Larsen" <spanget=at=virgil.ruc.dk>
Date: Thu, 20 Jan 2005 12:15:20 +0100

Dear CCL-community!

I became curious whether the disagreement in the current 
discussion on 'Orbitals and Reality' might originate in 
misleading or unclear presentations in introductory chemistry 
textbooks. Is the confusion introduced here, leading perhaps 
to the use of improper language in scientific articles, even 
by frontline researchers in leading journals?

First I looked up Zumdahl's "Chemical Principles" and found 
the following careful explanation of the situation. Can it be 
stated more clearly?

Yours, Jens >--<  

Steven S. Zumdahl: "Chemical Principles", Fourth Edition, 
Houghton Mifflin, Boston 2004. pp673-675: 

"14.6 Orbitals: Human Inventions

"In the treatment of the bonding and structure in molecules we 
have stressed that the descriptions we have given are models - 
and simple ones, at that. These models are extraordinarily 
valuable because they provide pictures in our minds of what 
molecules might look like and how they might behave. This 
helps us decide what questions to ask (what experiments to do) 
as we try to understand more completely the complicated 
behavior of matter. However, as valuable these pictures are, 
we must remember that they greatly oversimplify a very complex 
situation. We must realize that these models can give us a 
rather superficial view that is often highly misleading.  

"For example, after all of the talk about orbitals in the last 
several chapters, you probably have the distinct impression 
that orbitals actually exist. The truth is, they do not - at 
least not in the physical sense. Orbitals are mathematical 
functions - solutions to a modified Schrvdinger equation (the 
changes made to allow separation into independent electron 
equations).  

"Thus orbitals are mathematical tools we use to describe atoms 
and molecules. However, they have no physical reality in the 
sense that if you could look at the water molecule you would 
probably not "see" anything like the pictures we have shown in 
this book. These pictures merely help us visualize the 
theoretical imformation we have accumulated for water.  

(...)

"The point made here is ... to make sure that you appreciate 
the nature of models and that you recognize the difference 
between the information learned about matter from experiments 
and the information learned from theories. Because matter is 
so complex, we often tailor our theories to explain a limited 
area of nature so as to keep the theories simple enough to 
understand and use. However, it is very dangerous to assume 
that such a limited theory can then be used in a wider sense. 
We must be very careful to ask proper questions of our 
theories or we face the danger of being greatly misled."

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JENS SPANGET-LARSEN         Office:         +45 4674 2710
Department of Chemistry     Fax:            +45 4674 3011
Roskilde University (RUC)   Mobile:         +45 2320 6246
P.O.Box 260                 E-Mail:        spanget=at=ruc.dk
DK-4000 Roskilde, Denmark   http://virgil.ruc.dk/~spanget
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