Talk:Molecular orbital theory

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[edit] Simplify!

Cann somebody make this article so that anyone who does not have a backround in quantum theory and advanced math can understand it? Unfortunatly this goes for many science-related articles. They need to stop using terms that would only be known by people who proubably already know the theory.

--Lophoole 00:42, 12 October 2007 (UTC)

[edit] Wishlist

Here is a little wishlist I have...maybe someone has an idea of how to implement this:

  • Take CH4 and show how "sp3 hybridization" comes about from MO theory. In particular, highlight the fact that the MOs are one- and threefold degenerate, which from a superficial point of view, is contrary to the 4-fold degeneracy suggested by the hybridization picture. --HappyCamper 05:45, 7 January 2007 (UTC)
  • The hybrids are non-canonical MOs, that is, they are NOT eigenfunctions/eigenvectors of the Fock operator/matrix. Hybrids can be constructed by linear combination of a- and t-symmetry MOs, which have different orbital energies. Hence energies of hybrids are undefined. A remark of this type could be included in the article.--P.wormer 00:33, 18 March 2007 (UTC)

[edit] Query

Does this article have anything to add to molecular orbital?, candidate for merge in my view, what you are looking for in a qualititative way is represented in MO diagram but this article fails to provide a link. Also see my discussion with Smokefoot on this topic here V8rik 18:12, 7 January 2007 (UTC)

I am against merging. Molecular orbital theory, molecular orbital, and MO diagram are each their own topics. In your conversation with Smokefoot, as an example, you use the term “MO theory” as though this was common knowledge; yet until I started this page (a work-in-progress) there was nothing in WP that defined what MO theory was. The term MO theory is used all over WP; a redirect to molecular orbital doesn’t explain anything … everyone already knows what a molecular orbital is. The 2004 McGraw-Hill Concise Encyclopedia of Chemistry has a four-page section on "molecular orbital theory." If there is anything that needs to be merged or added to this article it is this section: Chemical bond#Molecular orbital theory; but I want, however, to make sure it is correct before I do so.
By the way, this article is almost brand new. Please give me some credit for trying to get it going. There are whole books and chapters written on specifically "molecular orbital theory". Also, aren’t you against mergers? You have a whole philosophy about this on your User page. Anyways, I am presently trying to build this article, bit by bit, so to show the contrast to that of valence bond theory. --Sadi Carnot 00:44, 8 January 2007 (UTC)
Hi Sadi Carnot! I am being grumpy again and please do continue with your good work. Yes I do maintain an anti-merge platform (not many supporters though) but I do occasionally merge. I will follow this page with interest. The point I am trying to make that in my view we can only get ahead in this Branch of theoretical chemistry if we at least introduce methane and also benzene MO treatment (more detail less overview). Also good point on the chemical bond article, the MO theory section there is too long and better placed here V8rik 18:22, 8 January 2007 (UTC)
V8rik, yes methane and benzene are good examples to have in the article. On your vote, I’ll do a quick merge of the some the MO material in the chemical bonding article. I apologize that I haven’t put any current basic molecular orbital theory into the article, but my current reading interest is on the “history of molecular orbital theory” (pre-1950s), i.e. how it came to be and whose ideas and shoulders it is built on. I’m sure I’ll chip in more later on the basics of MO theory (after I read a few more books on it), but for the present maybe you as well as others will help by adding a basic outline on current MO theory? --Sadi Carnot 03:46, 9 January 2007 (UTC)

I don't think the article needs to be merged, but as it it right now it says much about the early history of the theory but very little about the theory itself. The details about the MO theory are scattered in many articles; perhaps this one could serve as a starting point in the future, but in any case it would help to link to all of the relevant articles. Some examples of articles containing what you would find in a book about MO theory:

A good book on the topic, although a bit dated now, is Ab Initio Molecular Orbital Theory by Warren J. Hehre, Leo Radom, P. V. Schleyer, and John Pople. Wiley, 1986. Itub 14:59, 10 January 2007 (UTC)

[edit] Timeline

There is a lot of good work in the timeline, but most of if it is part of the early history of all of quantum mechanics, atomic physics, and nuclear physics. I would probably start the timeline of MO theory around 1926 and move the rest to another article on the history of quantum mechanics, but maybe that's just me. :) Itub 18:26, 8 January 2007 (UTC)

Itup, thanks for the comments and the related links. The book is a little too pricy ($150-used, $215-new) for me. The history of quantum mechanics needs to be a whole new article by itself. I was just looking at the Quantum mechanics#History section the other day and I was thinking about starting that page and moving much of that section there. Starting at a certain year, for either topic, however is a bad idea; it pre-assumes that the originator "thought" up the whole idea all by themselves. Most people, for example, have no idea that the concept of the "quantum" was actually derived and based the study of Boltzmann's entropy equation S = klogW (1872), i.e. that the derived roots of quantum mechanics are based on thermodynamics. --Sadi Carnot 03:46, 9 January 2007 (UTC)
For a history of quantum mechanics, I wouldn't object with starting with the cathode rays or even earlier. My reluctance to begin the history of MO theory that early is not because I think it was all created overnight, but just to avoid too much duplication, since MO theory is just a part of quantum mechanics and shares all the early history with QM. If we were writing a book on the MO theory, I wouldn't object either, because a book is much more self-contained than a Wikipedia article; however, here we can link very easily to other articles. You can mention the early history in an extremely condensed form and link to a more detailed article. Itub 16:35, 9 January 2007 (UTC)
Yes, I agree with you on the book point, but I'm not certain the QM and MO theory share "exactly" the same historical paths; certainly their is a lot of overlap. My point is that some people may not really care about reading a full account of quantum mechanics, and a lot of unrelated math. Thus, my long term goal is to eventually write two separate branch-off articles: History of molecular orbital theory and History of quantum mechanics. I'm sure I can write them both in time, we'll see? Also, there are dozens of articles that have historical origins to Planck's "quantum" energy units, but there's no need to merge them all together, we can have a separate history article for all of them, each with their own peculiarities. Another note is that my reading focus for these weeks is specifically molecular orbital theory, thus I try to contribute to only what I am reading about that week. So once this page gets too long, I'll move most of the history section to its own page. --Sadi Carnot 00:57, 10 January 2007 (UTC)

I agree with Itub's 8 January contribution at the top of what I have just made a new section. There is no need for history before 1926 as MO theory is quite meaningless without the Schrodinger equation. Maybe it can go somewhere else. A time line that deals with MO and VB as this one does, should perhaps go in quantum chemistry. It should not be here, as VB and MO theories are different. They are similar only in that they are both approximate solutions of the Schrodinger equation, and this article is about the MO approximation, not both. I suggest we have already got the history in its own section so the timeline table should go. It could be usefull in a broader "History of XXX" article. but I'm not sure what "XXX" should be. --Bduke 03:34, 10 January 2007 (UTC)

There you go Bduke, no more timeline. I’m just going to make a very strong personal note that this is the second time (here and at the valence bond article) that you have had problem with my sourced history contributions. --Sadi Carnot 07:31, 10 January 2007 (UTC)
I'm sorry you take it personally. I'm not opposed to history; far from it. However, history has to be relevant and focused in a science article. It is not just everything that has had some impact on the subject from way way back, however well sourced. I am happy to work with you in putting the timeline table into a new article on History of quantum chemistry. I actually know more of the history than most quantum chemists and have a colleague who knows even more. I have also lived through 50 years of it. What do you say? --Bduke 07:54, 10 January 2007 (UTC)

[edit] Ligand group orbitals

This idea should probably be somewhere too...just to register the idea for now. --HappyCamper 12:44, 9 January 2007 (UTC)

[edit] Image

Hello - we used to have this image on the article, but I checked the actual orbitals of this Methane, and they do not look too much like this, so I've removed it for now until we can find a better replacement. --HappyCamper 19:17, 11 January 2007 (UTC)

In MO theory, the shape of one molecular orbital of methane CH4, as determined by the molecular orbital wavefunction, is a mathematical combination of five atomic orbitals: one s-orbital on the carbon atom and four s-orbitals on the four hydrogen atoms. There are three other molecular orbitals which are triply degenerate. These symmetries can be determined by considering the character table for Td symmetry which the molecule of methane has.
In MO theory, the shape of one molecular orbital of methane CH4, as determined by the molecular orbital wavefunction, is a mathematical combination of five atomic orbitals: one s-orbital on the carbon atom and four s-orbitals on the four hydrogen atoms. There are three other molecular orbitals which are triply degenerate. These symmetries can be determined by considering the character table for Td symmetry which the molecule of methane has.

[edit] Notational questions

1. In text \psi and \chi are small Greek, as is usual for orbitals (one-electron functions). In equation capital Greek is used:

\Psi_j = \sum_{i=m}^{n} c_{ij} \Chi_i.

Why?

2. What is lower limit m? --P.wormer 00:20, 18 March 2007 (UTC)

You are right. I've fixed it. --Bduke 00:43, 18 March 2007 (UTC)