Talk:VSEPR theory

message: I'm reading through Zumdahl's 8th edition of Chemistry for fun. Chapter 8 covers VSEPR theory and Lewis structures, but after linear and trigonal planar, I have difficulty deriving the ideal bond angles (not bond angles for specific molecules like methane, etc.). Are there any resources that explain it well? Could it be added here somewhere? Just a person with an electrical engineering background trying to pick up basic chemistry and having difficulty with the harder stuff...  — Preceding unsigned comment added by 68.126.181.30 (talk) 19:56, 17 August 2011 (UTC)
replies: text: The hardest of the important ones is the ideal tetrahedron such as methane. I have now added a link to a proof for this case in the Examples section. Dirac66 (talk) 00:37, 8 May 2012 (UTC)
thread_title: Derivation of bond angles

message: 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)
thread_title: Removed text

message: "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)
thread_title: Steric number seven

message: 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)
thread_title: Rating

message: 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)
replies: text: Thanks for the suggestion; I'll take a look and see if I can import some of that material. Спасибо!—Tetracube (talk) 18:16, 24 September 2009 (UTC)
thread_title:  Needs expanding quite considerably 

message: Sorry, i had clicked the wrong thing and mis-typed. I apologise :-)   ♥♥ ΜÏΠЄSΓRΘΠ€ ♥♥ slurp me! 15:18, 8 April 2007 (UTC)
thread_title:  Apologies for the botched move 

message: 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)
thread_title:  Added text  

message: 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)
replies: text: 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)
replies: text: Thanks! Happy Editing! Jokermole (talk) 01:56, 22 January 2008 (UTC)
thread_title: Merged AXE method with VSEPR theory

message: 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)
replies: text: "The lede claims that "technically" it is pronounced ...oh, wait; it doesn't say how it is pronounced, just that it is not "vesper"."  This is incorrect, it DID say how it was pronounced - the phonetic pronunciation (which in this case is "vuh-seh-per", not "ves-per").  Unlike ket-sup/ket-chup, VSEPR is an acronym, meaning that it follows strictly phonetic pronunciation, which in this case is "vuh-seh-per".  VSE can't correctly be pronounced "ves" - its correct pronunciation is "vuh-seh".  PR's correct pronunciation is always "per", and no-one's arguing that it's anything different, so the correct pronunciation or "VSEPR" must be "vuh-seh-per". Whoop whoop pull up Bitching Betty | Averted crashes 19:27, 29 September 2013 (UTC)
replies: text: I have never heard anyone say vuh-seh-per. The most frequent spoken usage is to spell it out  (vee-ess-ee-pee-are), but ves-per is also common. Dirac66 (talk) 20:53, 29 September 2013 (UTC)
replies: text: I think "vesper" is most common in the US. Here in Australia I mostly hear it called "vee-ess-ee-pee-are" and I do not think I have ever heard it called "vuh-seh-per". --Bduke  (Discussion) 21:03, 29 September 2013 (UTC)
thread_title:  Also pronounced as Vesper 

message: I think that this table should be ordered by increasing the increasing steric number, as opposed to its current arrangement which isn't as intuitive if you are trying to learn it. --Rolen05 (talk) 20:28, 2 December 2008 (UTC)
thread_title: Organization of Molecular Type Table

message: The anion in tetramethylammonium pentafluoroxenate is an example of this geometry. I would add it but it needs a standard image- and the table sounds as if it may be reorganised.--Axiosaurus (talk) 14:49, 5 December 2008 (UTC)
thread_title:  Steric number  7,  AX<sub>5</sub>E<sub>2</sub> 

message: i changed the pictures on the trigonal planar and bent molecules grouping three.   they were mismatched.   i do not however know how to change the pictures so they now match bonding atoms and electron pairs  —Preceding unsigned comment added by 136.165.12.53 (talk) 03:20, 12 January 2010 (UTC)
replies: text: (I have moved this new section to the end.) In fact the table was correct so I have reverted your edit. However I have also added two sentences to explain that words such as "bent" refer only to the atomic positions (AX2) and not to the electron arrangement (AX2E). So in naming the pictures, the lone pairs are ignored. The second table is actually clearer as it shows both molecular geometry and electron arrangement.  Dirac66 (talk) 22:54, 12 January 2010 (UTC)
thread_title: Changed pictures

message: I've added a new See also, I dont know how to create an article but if someone know to do it, please, I think it is interesting:
Foundation
We begin by assuming a Lewis structure model for chemical bonding based on valence shell electron pair sharing and the octet rule. We thus assume the nuclear structure of the atom, and we further assume the existence of a valence shell of electrons in each atom which dominates the chemical behavior of that atom. A covalent chemical bond is formed when the two bonded atoms share a pair of valence shell electrons between them. In general, atoms of Groups IV through VII bond so as to complete an octet of valence shell electrons. A number of atoms, including C, N, O, P, and S, can form double or triple bonds as needed to complete an octet. We know that double bonds are generally stronger and have shorter lengths than single bonds, and triple bonds are stronger and shorter than double bonds.
Goals
We should expect that the properties of molecules, and correspondingly the substances which they comprise, should depend on the details of the structure and bonding in these molecules. The relationship between bonding, structure, and properties is comparatively simple in diatomic molecules, which contain two atoms only, e.g. HCl or O2. A polyatomic molecule contains more than two atoms. An example of the complexities which arise with polyatomic molecules is molecular geometry: how are the atoms in the molecule arranged with respect to one another? In a diatomic molecule, only a single molecular geometry is possible since the two atoms must lie on a line. However, with a triatomic molecule (three atoms), there are two possible geometries: the atoms may lie on a line, producing a linear molecule, or not, producing a bent molecule. In molecules with more than three atoms, there are many more possible geometries. What geometries are actually observed? What determines which geometry will be observed in a particular molecule? We seek a model which allows us to understand the observed geometries of molecules and thus to predict these geometries.
Once we have developed an understanding of the relationship between molecular structure and chemical bonding, we can attempt an understanding of the relationship of he structure and bonding in a polyatomic molecule to the physical and chemical properties we observe for those molecules.
Observation 1: Geometries of molecules
The geometry of a molecule includes a description of the arrangements of the atoms in the molecule. At a simple level, the molecular structure tells us which atoms are bonded to which. At a more detailed level, the geometry includes the lengths of all of these bonds, that is, the distances between the atoms which are bonded together, and the angles between pairs of bonds. For example, we find that in water, H2O, the two hydrogens are bonded to the oxygen and each O-H bond length is 95.72pm (where 1pm=10-12m). Furthermore, H2O is a bent molecule, with the H-O-H angle equal to 104.5°. (The measurement of these geometric properties is difficult, involving the measurement of the frequencies at which the molecule rotates in the gas phase. In molecules in crystalline form, the geometry of the molecule is revealed by irradiating the crystal with x-rays and analyzing the patterns formed as the x-rays diffract off of the crystal.)
Not all triatomic molecules are bent, however. As a common example, CO2 is a linear molecule. Larger polyatomics can have a variety of shapes, as illustrated in Figure 1. Ammonia, NH3, is a pyramid-shaped molecule, with the hydrogens in an equilateral triangle, the nitrogen above the plane of this triangle, and a H-N-H angle equal to 107°. The geometry of CH4 is that of a tetrahedron, with all H-C-H angles equal to 109.5°. (See also Figure 2(a).) Ethane, C2H6, has a geometry related to that of methane. The two carbons are bonded together, and each is bonded to three hydrogens. Each H-C-H angle is 109.5° and each H-C-C angle is 109.5°. By contrast, in ethene, C2H4, each H-C-H bond angle is 116.6° and each H-C-C bond angle is 121.7°. All six atoms of ethene lie in the same plane. Thus, ethene and ethane have very different geometries, despite the similarities in their molecular formulae.
Figure 1 Molecular Structures 
We begin our analysis of these geometries by noting that, in the molecules listed above which do not contain double or triple bonds (H2O, NH3, CH4and C2H6), the bond angles are very similar, each equal to or very close to the tetrahedral angle 109.5°. To account for the observed angle, we begin with our valence shell electron pair sharing model, and we note that, in the Lewis structures of these molecules, the central atom in each bond angle of these molecules contains four pairs of valence shell electrons. For methane and ethane, these four electron pairs are all shared with adjacent bonded atoms, whereas in
ammonia or water, one or two (respectively) of the electron pairs are not shared with any other atom. These unshared electron pairs are called lone pairs . Notice that, in the two molecules with no lone pairs, all bond angles are exactly equal to the tetrahedral angle, whereas the bond angles are only close in the molecules with lone pairs
One way to understand this result is based on the mutual repulsion of the negative charges on the valence shell electrons. Although the two electrons in each bonding pair must remain relatively close together in order to form the bond, different pairs of electrons should arrange themselves in such a way that the distances between the pairs are as large as possible. Focusing for the moment on methane, the four pairs of electrons must be equivalent to one another, since the four C-H bonds are equivalent, so we can assume that the electron pairs are all the same distance from the central carbon atom. How can we position four electron pairs at a fixed distance from the central atom but as far apart from one another as possible? A little reflection reveals that this question is equivalent to asking how to place four points on the surface of a sphere spread out from each other as far apart as possible. A bit of experimentation reveals that these four points must sit at the corners of a tetrahedron, an equilateral triangular pyramid, as may be seen in Figure 2(b). If the carbon atom is at the center of this tetrahedron and the four electron pairs at placed at the corners, then the hydrogen atoms also form a tetrahedron about the carbon. This is, as illustrated in Figure 2(a), the correct geometry of a methane molecule. The angle formed by any two corners of a tetrahedron and the central atom is 109.5°, exactly in agreement with the observed angle in methane. This model also works well in predicting the bond angles in ethane.
Figure 2 Tetrahedral Structure of Methane 
(a) The dotted lines illustrate that the hydrogens form a tetrahedron about the carbon atom. 
(b) The same tetrahedron is formed by placing four points on a sphere as far apart from one another as possible. 
We conclude that molecular geometry is determined by minimizing the mutual repulsion of the valence shell electron pairs. As such, this model of molecular geometry is often referred to as the valence shell electron pair repulsion (VSEPR) theory . For reasons that will become clear, extension of this model implies that a better name is the Electron Domain (ED) Theory .
This model also accounts, at least approximately, for the bond angles of H2O and NH3. These molecules are clearly not tetrahedral, like CH4, since neither contains the requisite five atoms to form the tetrahedron. However, each molecule does contain a central atom surrounded by four pairs of valence shell electrons. We expect from our Electron Domain model that those four pairs should be arrayed in a tetrahedron, without regard to whether they are bonding or lone-pair electrons. Then attaching the hydrogens (two for oxygen, three for nitrogen) produces a prediction of bond angles of 109.5°, very close indeed to the observed angles of 104.5° in H2O and 107° in NH3.
Note, however, that we do not describe the geometries of H2O and NH3 as "tetrahedral," since the atoms of the molecules do not form tetrahedrons, even if the valence shell electron pairs do. (It is worth noting that these angles are not exactly equal to 109.5°, as in methane. These deviations will be discussed later.)
We have developed the Electron Domain model to this point only for geometries of molecules with four pairs of valence shell electrons. However, there are a great variety of molecules in which atoms from Period 3 and beyond can have more than an octet of valence electrons. We consider two such molecules illustrated in Figure 3.
Figure 3 More Molecular Structures 
First, PCl5 is a stable gaseous compound in which the five chlorine atoms are each bonded to the phosphorous atom. Experiments reveal that the geometry of PCl5 is that of a trigonal bipyramid : three of the chlorine atoms form an equilateral triangle with the P atom in the center, and the other two chlorine atoms are on top of and below the P atom. Thus there must be 10 valence shell electrons around the phosphorous atom. Hence, phosphorous exhibits what is called an expanded valence in PCl5. Applying our Electron Domain model, we expect the five valence shell electron pairs to spread out optimally to minimize their repulsions. The required geometry can again be found by trying to place five points on the surface of a sphere with maximum distances amongst these points. A little experimentation reveals that this can be achieved by placing the five points to form a trigonal bipyramid. Hence, Electron Domain theory accounts for the geometry of PCl5.
Second, SF6 is a fairly unreactive gaseous compound in which all six fluorine atoms are bonded to the central sulfur atom. Again, it is clear that the octet rule is violated by the sulfur atom, which must therefore have an expanded valence. The observed geometry of SF6, as shown in Figure 3, is highly symmetric: all bond lengths are identical and all bond angles are 90°. The F atoms form an octahedron about the central S atom: four of the F atoms form a square with the S atom at the center, and the other two F atoms are above and below the S atom. To apply our Electron Domain model to understand this geometry, we must place six points, representing the six electron pairs about the central S atom, on the surface of a sphere with maximum distances between the points. The requisite geometry is found, in fact, to be that of an octahedron, in agreement with the observed geometry.
As an example of a molecule with an atom with less than an octet of valence shell electrons, we consider boron trichloride, BCl3. The geometry of BCl3 is also given in Figure 3: it is trigonal planar , with all four atoms lying in the same plane, and all Cl-B-Cl bond angles equal to 120°. The three Cl atoms form an equilateral triangle. The Boron atom has only three pairs of valence shell electrons in BCl3. In applying Electron Domain theory to understand this geometry, we must place three points on the surface of a sphere with maximum distance between points. We find that the three points form an equilateral triangle in a plane with the center of the sphere, so Electron Domain is again in accord with the observed geometry.
We conclude from these predictions and observations that the Electron Domain model is a reasonably accurate way to understand molecular geometries, even in molecules which violate the octet rule.
Observation 2: Molecules with Double or Triple Bonds
In each of the molecules considered up to this point, the electron pairs are either in single bonds or in lone pairs. In current form, the Electron Domain model does not account for the observed geometry of C2H4, in which each H-C-H bond angle is 116.6° and each H-C-C bond angle is 121.7° and all six atoms lie in the same plane. Each carbon atom in this molecule is surrounded by four pairs of electrons, all of which are involved in bonding, i.e. there are no lone pairs. However, the arrangement of these electron pairs, and thus the bonded atoms, about each carbon is not even approximately tetrahedral. Rather, the H-C-H and H-C-C bond angles are much closer to 120°, the angle which would be expected if three electron pairs were separated in the optimal arrangement, as just discussed for BCl3.
This observed geometry can be understood by re-examining the Lewis structure. Recall that, although there are four electron pairs about each carbon atom, two of these pairs form a double bond between the carbon atoms. It is tempting to assume that these four electron pairs are forced apart to form a tetrahedron as in previous molecules. However, if this were this case, the two pairs involved in the double bond would be separated by an angle of 109.5° which would make it impossible for both pairs to be localized between the carbon atoms. To preserve the double bond, we must assume that the two electron pairs in the double bond remain in the same vicinity. Given this assumption, separating the three independent groups of electron pairs about a carbon atom produces an expectation that all three pairs should lie in the same plane as the carbon atom, separated by 120° angles. This agrees very closely with the observed bond angles. We conclude that the our model can be extended to understanding the geometries of molecules with double (or triple) bonds by treating the multiple bond as two electron pairs confined to a single domain. It is for this reason that we refer to the model as Electron Domain theory.
Applied in this form, Electron Domain theory can help us understand the linear geometry of CO2. Again, there are four electron pairs in the valence shell of the carbon atom, but these are grouped into only two domains of two electron pairs each, corresponding to the two C=O double bonds. Minimizing the repulsion between these two domains forces the oxygen atoms to directly opposite sides of the carbon, producing a linear molecule. Similar reasoning using Electron Domain theory as applied to triple bonds correctly predicts that acetylene, HCCH, is a linear molecule. If the electron pairs in the triple bond are treated as a single domain, then each carbon atom has only two domains each. Forcing these domains to opposite sides from one another accurately predicts 180° H-C-C bond angles.
Observation 3: Distortions from Expected Geometries
It is interesting to note that some molecular geometries (CH4, CO2, HCCH) are exactly predicted by the Electron Domain model, whereas in other molecules, the model predictions are only approximately correct. For examples, the observed angles in ammonia and water each differ slightly from the tetrahedral angle. Here again, there are four pairs of valence shell electrons about the central atoms. As such, it is reasonable to conclude that the bond angles are determined by the mutual repulsion of these electron pairs, and are thus expected to be 109.5°, which is close but not exact.
One clue as to a possible reason for the discrepancy is that the bond angles in ammonia and water are both less than 109.5°. Another is that both ammonia and water molecules have lone pair electrons, whereas there are no lone pairs in a methane molecule, for which the Electron Domain prediction is exact. Moreover, the bond angle in water, with two lone pairs, is less than the bond angles in ammonia, with a single lone pair. We can straightforwardly conclude from these observations that the lone pairs of electrons must produce a greater repulsive effect than do the bonded pairs. Thus, in ammonia, the three bonded pairs of electrons are forced together slightly compared to those in methane, due to the greater repulsive effect of the lone pair. Likewise, in water, the two bonded pairs of electrons are even further forced together by the two lone pairs of electrons.
This model accounts for the comparative bond angles observed experimentally in these molecules. The valence shell electron pairs repel one another, establishing the geometry in which the energy of their interaction is minimized. Lone pair electrons apparently generate a greater repulsion, thus slightly reducing the angles between the bonded pairs of electrons. Although this model accounts for the observed geometries, why should lone pair electrons generate a greater repulsive effect? We must guess at a qualitative answer to this question, since we have no description at this point for where the valence shell electron pairs actually are or what it means to share an electron pair. We can assume, however, that a pair of electrons shared by two atoms must be located somewhere between the two nuclei, otherwise our concept of "sharing" is quite meaningless. Therefore, the powerful tendency of the two electrons in the pair to repel one another must be significantly offset by the localization of these electrons between the two nuclei which share them. By contrast, a lone pair of electrons need not be so localized, since there is no second nucleus to draw them into the same vicinity. Thus more free to move about the central atom, these lone pair electrons must have a more significant repulsive effect on the other pairs of electrons.
These ideas can be extended by more closely examining the geometry of ethene, C2H4 . Recall that each H-C-H bond angle is 116.6° and each H-C-C bond angle is 121.7°, whereas the Electron Domain theory prediction is for bond angles exactly equal to 120°. We can understand why the H-C-H bond angle is slightly less than 120° by assuming that the two pairs of electrons in the C=C double bond produce a greater repulsive effect than do either of the single pairs of electrons in the C-H single bonds. The result of this greater repulsion is a slight "pinching" of the H-C-H bond angle to less than 120°.
The concept that lone pair electrons produce a greater repulsive effect than do bonded pairs can be used to understand other interesting molecular geometries. Sulfur tetrafluoride, SF4, is a particularly interesting example, shown in Figure 4.
Figure 4 Molecular Structure of SF4 
Note that two of the fluorines form close to a straight line with the central sulfur atom, but the other two are approximately perpendicular to the first two and at an angle of 101.5° to each other. Viewed sideways, this structure looks something like a seesaw.
To account for this structure, we first prepare a Lewis structure. We find that each fluorine atom is singly bonded to the sulfur atom, and that there is a lone pair of electrons on the sulfur. Thus, with five electron pairs around the central atom, we expect the electrons to arrange themselves in a trigonal bipyramid, similar to the arrangement in PCl5 in Figure 3. In this case, however, the fluorine atoms and the lone pair could be arranged in two different ways with two different resultant molecular structures. The lone pair can either go on the axis of the trigonal bipyramid (i.e. “above” the sulfur) or on the equator of the bipyramid (i.e. “beside” the sulfur).
The actual molecular structure in Figure 4 shows clearly that the lone pair goes on the equatorial position. This can be understood if we assume that the lone pair produces a greater repulsive effect than do the bonded pairs. With this assumption, we can deduce that the lone pair should be placed in the trigonal bipyramidal arrangement as far as possible from the bonded pairs. The equatorial position does a better job of this, since only two bonding pairs of electrons are at approximately 90° angles from the lone pair in this position. By contrast, a lone pair in the axial position is approximately 90° away from three bonding pairs. Therefore, our Electron Domain model assumptions are consistent with the observed geometry of SF4. Note that these assumptions also correctly predict the observed distortions away from the 180° and 120° angles which would be predicted by a trigonal bipyramidal arrangement of the five electron pairs.
[end of proposed text]
This looks very much as if it is copied directly from somewhere and would therefore be a copyright violation. In what sense is this topic notable enough for a separate article rather than being incorporated in one or more other article?  --Bduke  (Discussion) 20:35, 1 February 2010 (UTC)
thread_title: Electron Domain

message: Today we seem to have a disagreement as to where put XeF82- in the table of geometries and examples. Does it go on the line for steric number 8 or 9? As discussed above, the problem is that although simple electron counting (Lewis structure) gives 9 pairs (8 bonds + 1 lone pair), the experimental geometry is the square antiprism expected for 8 pairs. That is, the VSEPR theory gives the wrong answer for this molecule, as first noted in 1971 by Peterson et al. who determined the experimental structure.
So I think it is misleading to put this molecule on EITHER line. Placing it at n=8 is misleading because the VSEPR model is based on simple electron counting which gives n=9. And placing it at n=9 is misleading because it suggests that VSEPR predicts a square antiprism for n=9 and one lone pair, which is not true. (I think - if it does we need a reference).
I think the answer is to remove this molecule as an example in the tables, which should only use examples for which VSEPR predicts the correct geometry. Exceptions are dealt with in the next section where they are clearly labelled as such. We can add XeF82- as an exception after XeF6, which is octahedral for somewhat similar reasons. Dirac66 (talk) 21:40, 6 May 2012 (UTC)
replies: text: Double sharp (talk) 03:38, 11 May 2012 (UTC)
replies: text: Thanks to Double sharp and I agree with your edits for XeF82-. However they have now been reverted by Whoop whoop pull up with the edit summaries "Rv unexplained removal of content" and "Rm nonsense". To Whoop whoop pull up: the removal was in fact explained in this section of the talk page, so please respond to the above comments and explain why you think that Double sharp's edit is nonsense. While I have myself on other occasions used similar edit summaries, I would not do so when the edits have been justified on the talk page. Dirac66 (talk) 19:28, 12 May 2012 (UTC)
replies: text: Here is the reason why.  Consider a molecule with a capped square antiprismatic geometry.  Now ignore the ligand capping the square antiprism.  What do you get?  A slightly distorted square antiprism.  What is the geometry of XeF82-?  A slightly distorted square antiprism—which is exactly the geometry predicted by VSEPR theory for an AX8E1 molecule! Whoop whoop pull up Bitching Betty | Averted crashes 22:32, 12 May 2012 (UTC)
replies: text: Well, that was explained quite well in the edit summaries; ignoring the lone pair on the octafluoroxenate ion is a special case that confuses our readers.--Jasper Deng (talk) 22:37, 12 May 2012 (UTC)
replies: text: So who do you agree with? Whoop whoop pull up Bitching Betty | Averted crashes 22:43, 12 May 2012 (UTC)
replies: text: Dirac66 - after all, I was the one who noted the confusion about this particular ion.--Jasper Deng (talk) 22:44, 12 May 2012 (UTC)
replies: text: So you're one of the ones being confused?  Read my post above and see why I am right and he is wrong. Whoop whoop pull up Bitching Betty | Averted crashes 22:49, 12 May 2012 (UTC)
replies: text: Most people cannot visualize the shape. Even if you are technically correct, the shapes aren't exactly the same, and therefore, this ion is a bad example of this geometry.--Jasper Deng (talk) 22:52, 12 May 2012 (UTC)
replies: text: Then what would be a good example of an AX8E1 molecule? Whoop whoop pull up Bitching Betty | Averted crashes 23:58, 12 May 2012 (UTC)
replies: text: Perhaps ReH84-, if existing? Just any complex that has a steric # of 9.--Jasper Deng (talk) 00:21, 13 May 2012 (UTC)
thread_title: Don't use this exception as an example in the tables

message: Today again some of the blue (working) links in the tables have been replaced by red (broken) links. For example, square antiprism is blue and leads to a real article), but  has been replaced by square antiprismatic molecular geometry which is red and leads to an error message. Well, an invitation to create your own article. This is not really helpful to the 99.9% of readers (there were 23K page views in the last 30 days) who have no intention of creating their own article on this subject, but may just want to know what a square antiprism looks like. The square antiprism article at least does show a picture and some discussion, even if it is not an article with molecular geometry in its title.
So I am going to revert the latest removal and restore the link to square antiprism, as well as the link to gyroelongated square pyramid inserted by Double Sharp earlier today. Also I am going to replace the red link to pentagonal planar molecular geometry by a simple link to Pentagon, again to illustrate the term as well as possible using an existing article. Please do not restore the red linked terms ... unless you are actually going to write the missing articles to which they point. Dirac66 (talk) 02:53, 4 May 2012 (UTC)
replies: text: I've restored the blue links. Double sharp (talk) 03:00, 4 May 2012 (UTC)
replies: text: The articles have been written and I have restored the links to them. Whoop whoop pull up Bitching Betty | Averted crashes 12:53, 12 May 2012 (UTC)
replies: text: OK, now these links lead to useful information. Dirac66 (talk) 19:10, 12 May 2012 (UTC)
thread_title:  Red links do not help the reader 

message: The most recent controversies are about the inclusion of diatomics in the article and the likely geometries for steric numbers 10, 11 and 12.
I agree with Whoop Whoop Pull Up that diatomic molecules do not belong in this article. The reason is that VSEPR theory is not required to find the geometry of a diatomic molecule, which must be linear because any two points define a line. This was obvious long before VSEPR and even before electrons were known to exist. So diatomics are not an example of the use of VSEPR theory, even if some general chemistry books include them in a table of molecular geometries.
For n = 10, 11 and 12 however, I cannot agree with Whoop Whoop Pull Up's repeated reversion of the edits by Double Sharp. Wikipedia is based on sources - see for example WP:Sources which says that any material challenged or likely to be challenged must be attributed to a reliable published source. The geometries given by each of these editors for n = 10-12 have been challenged by the other, but only Double Sharp has given a source. Whoop Whoop Pull Up has given no source or even real reasoning other than to say in his edit summaries that I am right and you are wrong (though not in those words). 
Since we have a source for one set of geometries and not the other, we must use the sourced geometries. And even if Whoop Whoop Pull Up does find a future source for the other set of geometries, then we would have conflicting sources so we would mention both opinions.
Also in his latest edit, Whoop Whoop Pull Up has just deleted Double Sharp's source without explanation. Since the source is a standard textbook, it is not acceptable to just remove it because it does not support your point of view. 
In view of the above, I will now restore Double Sharp's last version for n = 10-12 with the source, but not the diatomic molecules.  Dirac66 (talk) 01:02, 14 June 2012 (UTC)
thread_title:  Latest edit wars - Diatomics and steric numbers 10, 11, 12 

message: This is quoted as an exception to VSEPR-- it is unreferenced--the fact that the structure details probably relate to the solid state could account for the deviation from linearity- mercury fulminate may have had its structure determined in the vapour phase which would be a real tour de force, and if so a bent configuration found there would be relevant. I do not have the access to journals to get to the bottom of this. Axiosaurus (talk) 16:52, 19 June 2013 (UTC)
replies: text: You are right – it's not bent: see . Removed, and added a  tag for the other unreferenced example there. Double sharp (talk) 15:35, 22 June 2013 (UTC)
thread_title:  mercury fulminate - example of bent geometry around carbon. 

message: *Trigonal prismatic – W(CH3)6, [Zr(CH3)6]2−
*Capped trigonal prismatic – [NbF7]2−
*Capped octahedral – [W(CO4Br3]−
*Cubic – 
*Dodecahedral (snub disphenoid) – [Mo(CN)8]3−
*Not named? (looks like a distorted icosahedron) – a cerium nitrato complex
All from http://www.d.umn.edu/~pkiprof/ChemWebV2/
Are these even part of VSEPR theory? Or are most of these just exceptional cases like W(CH3)6 when VSEPR fails to predict the correct geometry? Double sharp (talk) 14:30, 11 May 2014 (UTC)
replies: text: These are all transition metal compounds, which are mentioned as the first group in the section on Exceptions. In fact your first example, W(CH3)6, is the first molecule mentioned in the Exceptions section, and its geometry is described in its own article. Dirac66 (talk) 18:03, 11 May 2014 (UTC)
replies: text: Ah, OK. Perhaps more of these ought to be mentioned as examples of unusual geometries somewhere, though. Double sharp (talk) 08:25, 12 May 2014 (UTC)
thread_title:  Some geometries not covered in this article (or indeed elsewhere on WP, AFAIK) 

message: The missing talk entries from 12 May to this date?  Asked because I recall having posted in talk, extensively, while I was editing last night, and at least that Talk Section appears to have been deleted.  Please reply, knowledgable/responsible parties. Meanwhile, I am calling it to attention of admins.  Cheer.  Le Prof  Leprof 7272 (talk) 01:07, 31 May 2014 (UTC)
replies: text: Well, the page history there shows no posts to the talk page between November 2013 and the end of April 2014, and no removals or deletions - there isn't anything missing from the page. - The Bushranger One ping only 01:34, 31 May 2014 (UTC)
replies: text: Must have gotten lost then Bush, thanks for checking. Was not sure if there was an administrative way to "disappear" entries without leaving a trace that editors could follow. Will post about the edits, anew. Cheers.  Le Prof Leprof 7272 (talk) 02:03, 1 June 2014 (UTC)
thread_title:  Could someone please explain 

message: I would suggest to rename the "Exceptions". Half of the examples are interesting cases, items under discussion, but not the exceptions. P99am (talk) 09:06, 16 October 2014 (UTC)
replies: text: What name would you suggest for the "Exceptions" section? And which examples in that section are not exceptions? Dirac66 (talk) 02:25, 17 October 2014 (UTC)
thread_title: Exceptions

message: (This isn't a suggestion for the article, but rather for octadecahedron and edge-contracted icosahedron; I'm putting it here because the issue is a bit larger, but is not a problem for all the other polyhedron names; and also because I think this page would be quite a bit more watched.)
The names used by chemists and mathematicians for these polyhedra seem to be different:
* The chemist's trigonal is more often triangular among mathematicians (although I've seen the trigonal forms too);
* The chemist's seesaw is a mathematician's disphenoid;
* The chemist's capped is a mathematician's augmented;
* The chemist's dodecadeltahedron is a mathematician's snub disphenoid;
* The chemist's capped square antiprism and bicapped square antiprism are a mathematician's gyroelongated square pyramid and gyroelongated square bipyramid;
* The chemist's octadecahedron doesn't appear to have a standard name among mathematicians, but I haven't seen octadecahedron used in mathematics; a reasonable name using mathematical terminology would be an edge-contracted icosahedron.
This makes for great fun for the article titles! The obvious solution, I guess, is for the chemistry articles to primarily use the chemists' names (but cross-referencing the mathematicians' ones at the first mention), and for the mathematics articles to do the opposite. For the rarer molecular shapes (like bicapped square antiprismatic), the mathematicians' usage is probably primary.
The only trouble comes for the octadecahedron, which is barely mentioned at all in mathematics (because it cannot be constructed using equilateral triangles, it doesn't get an invitation to the Royal Deltahedron Club), and so its main appearance is in chemistry (where equilateral triangles aren't necessary)! However, the article uses an extrapolated mathematical name (i.e. a name that would be expected, but in practice I haven't seen used much if at all in mathematics), and reserves octadecahedron for its mathematical meaning (any polyhedron with 18 faces!), never mind that the name octadecahedron is very rarely encountered in mathematics because there it's so ambiguous, possibly referring to over 1014 topologically distinct shapes!
Per WP:PRIMARYTOPIC I think the subject of octadecahedron probably ought to be the [B11H11]2− structure, as it is in chemistry, with a brief note about the other 18-faced polyhedra at the bottom. Double sharp (talk) 07:37, 28 March 2015 (UTC)
replies: text: P.S. Oh, this just gets better. About dodecadeltahedron; in chemistry this means the snub disphenoid but in mathematics it more often means the hexagonal bipyramid according to the latter article. Which is the primary use? In the meantime I've made dodecadeltahedron a disambiguation page listing both meanings. Double sharp (talk) 07:41, 28 March 2015 (UTC)
replies: text: Bravo for your efforts to sort out all this mess. Presumably the chemists who determined the more obscure molecular geometries just went ahead and named them without checking the mathematical literature. I agree with your approach to the problem - use the usual names in each field but cross-reference the other names as well. Dirac66 (talk) 18:31, 29 March 2015 (UTC)
replies: text: Heads-up on the broken citation.--Officer781 (talk) 11:30, 30 March 2015 (UTC)
replies: text: I have turned dodecadeltahedron into a redirect to snub disphenoid, as I cannot find any example of the purported mathematical usage mentioned above outside Wikipedia (I have removed that from the hexagonal bipyramid article as well). Double sharp (talk) 14:47, 19 September 2018 (UTC)
thread_title:  An interesting issue re the names 

message: OK, we now have the following short concluding paragraph:
:The VSEPR theory places each pair of valence electrons in a bond or a lone pair found in a local region of the molecule based on the Pauli exclusion principle. While this is frequently taught in chemistry textbooks in conjunction with orbital models such as orbital hybridisation and molecular orbital theory, the approach is completely different. Electron pairs can constitute degrees of repulsion independent of their valence configuration, which is why bonding pairs are treated identically regardless of the bond order and certain molecules can have more than 4 electron pairs regardless of the octet rule.
I think the first two sentences are clear and quite satisfactory. However the final sentence now seems to be the most confusing in the entire article. What is a degree of repulsion? And what exactly is being claimed in the which is why clause? Can this be rewritten more clearly? If not, perhaps we should just delete the sentence and end the article with the approach is completely different.— Preceding unsigned comment added by Dirac66 (talk • contribs) 
:Removed. Although I find this to make the paragraph sound like a cliffhanger. Would probably want to explain how the approaches are different.--Officer781 (talk) 03:19, 1 April 2015 (UTC)
thread_title: Confusing final sentence

message: After digging through VSEPR papers I realized Gillespie does mention a section in one of his papers that exceptions transition metal molecules can be explained in that the ligands are strongly-interacting with the atomic core and produce electron pairs that occupy two regions on opposite sides of the atom. Sounds too similar to sd hybrids but I feel that amounts to an explanation so I've rewritten it and removed it as an exception (which is meant to show the limiting areas of VSEPR without a sufficiently convincing explanation).--Officer781 (talk) 02:19, 17 April 2015 (UTC)
thread_title:  Transition metal molecules 

message: This article so far only distinguishes bonding pairs from lone pairs. VSEPR has an analogue of Bent's rule which should be introduced: electron pairs of more electronegative substituents constitute greater repulsion. Lone pairs are a special case of this rule. Also, bond order affects degree of repulsion. Putting this as a to-do for myself and in case anyone else has any input or wants to give a go.--Officer781 (talk) 14:02, 17 April 2015 (UTC)
thread_title:  deviations from ideal angles 

message: The user Haminoon who I suspect has no formal chemistry training keeps reverting my edit concerning using a formula to to predict lone pairs as appose to using a Lewis diagram.
View the edit here:
https://en.wikipedia.org/w/index.php?title=VSEPR_theory&oldid=prev&diff=685751252
:I have taught university chemistry and I agree with Haminoon that this method does not belong in the Wikipedia article. The task of Wikipedia is to present subjects as described in widely used textbooks, rather than simplified versions on obscure web sites, which is presumably what Haminoon means by not notable. And in this case there is a good reason why textbooks do not use this simplified method: it only works for atoms with a single central atom surrounded by either all hydrogens or no hydrogens. For a molecule such as CHCl3, one would have to specify that the number of hydrogens is multiplied by two and the number of other non-central atoms by eight. Worse, for molecules with more than one central atom (e.g. ethylene, acetic acid, benzene, S2F10, etc. etc.) there is no simple general formula and the best advice to students is to draw a Lewis structure. So the textbook authors have decided that it is simpler to skip the shortcut which only works sometimes and just present the one method which works most often.
:I will re-delete the paragraph in question. Dirac66 (talk) 00:47, 15 October 2015 (UTC)
replies: text: Agreed. Also for Unit388's information, note that changing the method on this talk page is original research which is not allowed in Wikipedia, partly because the ideas have not been tested by the usual processes in the scientific literature such as refereeing and reaction by others. In this case your new fix is quickly shown to be incorrect: for S2F10 L = (41-(5x8)) x 2 = 2 lone pair electrons or one lone pair. However the Lewis structure shows that there is no lone pair but instead an S-S single bond which is not included in your calculation. Similarly for ethylene, L = (6 - (2x2)) x 2 = 4 or two lone pairs. Again there are no lone pairs but rather a C=C double bond. This illustrates why we want reliable sources. Dirac66 (talk) 11:37, 15 October 2015 (UTC)
thread_title:  Unrelated editor reverting edits 

message: :
:
To Officer781: On 23 April 2015 you wrote the following first sentence in the section Transition metal molecules: Many transition metal compounds have unusual geometries, which can be ascribed to absence of valence shell lone pairs and ligand bonding interaction with the d-subshell. As editor Norbornene pointed out yesterday, this can be interpreted in 2 ways: it can be read which can be ascribed to absence of valence shell lone pairs and TO ligand bonding interactions ..., meaning that the ligand bonding interactions are PRESENT. Or it can be read as which can be ascribed to absence of valence shell lone pairs and OF ligand bonding interactions ..., meaning that the ligand bonding interactions are ABSENT. Norbornene could not figure out which is correct, and neither can I even after looking briefly through the source paper by Kaupp. So could I ask you to decide which you meant, and then to clarify the sentence, perhaps by adding TO or OF as appropriate. Thanks in advance. Dirac66 (talk) 01:20, 14 August 2016 (UTC)
replies: text: Clarified. Hopefully this clears it up. Do ping me if there are any further issues.--Officer781 (talk) 02:38, 15 August 2016 (UTC)
thread_title:  Ambiguous sentence re transtition metal molecules 

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thread_title:  External links modified 

message: ভিএসইপিআর তত্ত্ব(VSEPR Theory- Valence Shell Electron Pair Theory") হল একটি এমন তত্ত্ব যার মাধ্যমে কোনো রাসায়নিক গঠনের বা যৌগের বিভিন্ন রকমের প্রধান চারিত্রিক বৈশিষ্ট্য যেমন-ইলেকট্রন ঘনত্ব,অণুর গঠন,বন্ধন ক্ষমতা ইত‍্যাদি নির্ণয় করা সম্ভব। Aishik Datta (talk) 20:42, 25 August 2020 (UTC)
thread_title:  ভিএসইপিআর তত্ত্ব(যোজ‍্যতা শক্তিস্তর ইলেকট্রন জোড় বিকর্ষণ তত্ত্ব) 

message: I propose to merge steric number here as the rationale is pretty much the same as Talk:AXE method. Basically, the term is only used in the context of VSEPR and as such does not warrant a separate page. Pinging  and  for comment.--Officer781 (talk) 11:09, 5 September 2020 (UTC)
replies: text: Yes, I agree. I think Steric number should be one section of this article on VSEPR theory, perhaps following Overview. And I also notice that the article on Steric number is now completely unreferenced. I will now add a reference for the definition of steric number, which can of course be transferred to the new merged article. Dirac66 (talk) 15:17, 5 September 2020 (UTC)
replies: text:  Thanks. I have now merged the article here as a section following Overview.--Officer781 (talk) 00:00, 6 September 2020 (UTC)
thread_title:  Merger proposal