Talk:VSEPR theory
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[edit] Removed text
I removed the following text because I didn't know where it would fit better in the article. Please add it back if you figure out.
- If the connectivity, bond lengths, bond angles and torsional angles are found, a molecules exact geometry is known. For any non-linear molecule with N atoms, 3N - 6 internal coordinates need to be specified in order to know the exact geometry of the molecule.
-- Rune Welsh ταλκ 21:40, July 28, 2005 (UTC)
Is this correct? I always thought that VSEPR was part of Valence Bond Theory. I thought sigma and pi bonding were part of Molecular Orbital Theory.
"VSEPR theory is usually compared and contrasted with valence bond theory, which addresses molecular shape through orbitals that are energetically accessible for bonding. Valence bond theory concerns itself with the formation of sigma and pi bonds."
Captain Video 20:52, 9 August 2006 (UTC)Captain Video
VSEPR theory is not part of Valence Bond theory. See what the original authors od VSEPR say. It does however suggest similarities to some people. Sigma and pi bonding are part of both valence bond and molecular orbital approaches. I would keep the first sentence and delete the second. --Bduke 23:39, 9 August 2006 (UTC)
[edit] Steric number seven
"In fact, a steric number of seven is possible, but it occurs in uncommon compounds such as xenon hexafluoride. The base geometry for this is pentagonal bipyramidal. The trend for this configuration is the same as for the octahedral configuration: the first nonbonding electron domain would be in the axial position, making the actual molecular geometry pentagonal pyramidal."
This text is inaccurate - xenon hexaflouride is in fact a semi-octahedral geometry with a lone pair on it. It is indeed not pentagonal bipyramidal at all. —Preceding unsigned comment added by 143.167.238.53 (talk) 17:13, 8 March 2008 (UTC)
XeF6 was indeed an incorrect example, but IF7 (with 0 lone pairs) is a valid example of pentagonal bipyramidal geometry. There are also several examples of anions with a central transition metal which have steric numbers 7, 8 and higher which can be included in the article. Dirac66 (talk) 18:52, 8 March 2008 (UTC)
I have modified the paragraph to use IF7 as the example after mistakenly reverting the edit by the anon. --Bduke (talk) 00:59, 9 March 2008 (UTC)
[edit] More removed text
I removed the following as unsourced, and lacking in good grammar. I'm no expert in VSEPR so I can't make a decision as to whether it is acceptable/correct or not. Anyone with more experience is invited to correct and reinsert material where appropriate.Hyenaste (tell) 22:07, 16 August 2006 (UTC)
- It must be emphasised that the VESPR is not really a theory, in spite of its often being referred to in this manner. It is a convenient method to get a rough idea about what the probable shape of a molecule might be. The actual shape that real molecules achieve is the result of quantum mechanics and the geometry of orbitals. One aspect of it that is particularly bad from a theoretical standpoint is the idea that "non bonding electrons repel more strongly than bonded ones." The real reason that stibine (SbH3) exhibits 90 degree bond angles is because the antimony (Sb) atom uses its p orbitals for forming the Sb-H bonds, and these are mutually perpendicular. Ammonia exhibits a 107 degree bond angle because the energy difference between 2s and 2p orbitals are small so hybridised orbitals can form. For s and p hybridised bonds the bond angle is given by acos(-s/p) where s is the "s" fraction of the orbital and p is the "p" component.
[edit] Rating
I've given the article a quick assessment after adding the chemistry template. I only gave it a start class rating since it's quite short and lacks structure (sections). A little on the history of the theory would help with both these issues, for example. It's quite a good start class article all the same, maybe even a low B-class. Richard001 04:21, 16 January 2007 (UTC)
How is this possible?
[edit] Needs expanding quite considerably
There's quite a lot missing from the article; character of compounds and likely axial and equatorial postions of bonding pairs, multiple bonds, etc. Anyone up for a huge drive on this article, because it's pretty important in bonding theory 
♥♥ ΜÏΠЄSΓRΘΠ€ ♥♥ slurp me! 12:06, 5 April 2007 (UTC)
[edit] Apologies for the botched move
Sorry, i had clicked the wrong thing and mis-typed. I apologise :-) ♥♥ ΜÏΠЄSΓRΘΠ€ ♥♥ slurp me! 15:18, 8 April 2007 (UTC)
[edit] Added text
I added the following text
"i) Pairs of electrons in the valence shell of a central atom repel each other. ii) These pairs of electrons tend to occupy positions in space that minimize repulsions and maximise the distance of separation between them. iii) The valence shell is taken as a sphere with electron pairs localising on the spherical surface at maximum distance from one another. iv) A multiple bond is treated as if it is a single electron pair and the two or three electron pairs of a multiple bond are treated as a single super pair. v) Where two or more resonance structures can depict a molecule the VSEPR model is applicable to any such structure."
thoug i am not an expert at this theory i am a student of it. if this is found to be wrong please forgive me and without hesitation delete this section hat i created.
I am not good at organising. so please any of you experts please organise it. thank you.--Bandaruvamsi1991 15:41, 28 September 2007 (UTC)
[edit] Merged AXE method with VSEPR theory
As has been suggested by User:Bduke and others, I have merged the two articles. It will now redirect from the old article to here. Jokermole (talk) 05:24, 21 January 2008 (UTC)
- A very good idea as AXE is just a notation for applying the VSEPR theory. The only problem was that you kept two identical copies of the table which appeared in both old articles, so I have deleted one copy of the table. Dirac66 (talk) 14:16, 21 January 2008 (UTC)
[edit] Also pronounced as Vesper
I know that it is hard to take seriously the anonymous numbered editor who earlier today first inserted HAHA and then two minutes later inserted "ALSO PRONOUNCED AS VESPER!!!!" all in capitals with 4 exclamation marks into the first line of the article. However I also know many chemists who do pronounce it informally as "vesper", and on picking up the first general chemistry book which comes to hand (Petrucci, Harwood and Herring "General Chemistry: Principles and Modern Applications", Prentice-Hall 8th edn 2002, p.410) I find that the theory is introduced as "the valence-shell electron-pair repulsion theory (written VSEPR and pronounced 'vesper')".
So perhaps it would be a good idea to let readers know that yes, this theory is the same "vesper" they have heard their profs mention, although without the capitals and the exclamation marks and perhaps not on the first line. I suggest modifying the second sentence, which also mentions an alternate name, to read "The theory is also called the Gillespie-Nyholm theory after the two main developers, and VSEPR is sometimes pronounced as "vesper" which is easier to say." Other opinions please. Dirac66 (talk) 16:44, 19 March 2008 (UTC)
No objection after 1 week so I have done it. And I have also added an entry to the page Vespers (disambiguation), where some non-chemist who hears (rather than reads) the term might look. Dirac66 (talk) 01:41, 26 March 2008 (UTC)
