Unravelling the Mystery of VSEPR Theory

[Cheman]

VSEPR Theory...

I am completely at ease with being able to use VSEPR theory to answer questions, etc, but I just can't get my head round why it actually happens? All I am told is "electron clouds repel each other to be as far apart as possible", but this seems to completely disagree with the idea of orbitals, etc - the places where elctrons must be. (95% of the time of course... ) The electron pairs are present in orbital which exist in certain places around the nuncleus - why would these move? Thats treating them as if they are solid themselves, like balloons - which they are not.

Is the answer to this a bit more advanced than the "electron clouds repel each other to be as far apart as possible" statement let's on? (ie - does it result from hybridization, etc? )

Thanks in advance.

 

[Gokul43201]

Yes, it is due to hybridization.

When orbitals hybridize, they "lose their identity". A more detailed answer will take a lot of time and energy, so I'll wait for others to chip in first.

 

[dextercioby]

Yes,it is a bit more advanced.It has to with the fact that QM governs fundamental chemistry.And the chemical bond and the geometry of the molecules.The electron pair repulsion is natural and comes from thefact that these electrons are charged particles with the same sign and it is natural to repel each other.The hamiltonian term containing these Coulomb potentials becomes significantly important and cannot be treated as a perturbation.
So the theory of Gillespie is very well physically founded.

Daniel.

 

[chem_tr]

I would like to say something about this, but a bit less "advanced" about the area... In VSEPR theory, I think the "restlessness" of non-bonding electron pairs is much more than bonding electrons. So, if a non-bonding electron pair is present in the molecule, this will cause the structure to deviate from ideal geometry, see ammonia and water, for example. If we could isolate the cation of ammonia, say, NH₃⁺, (note that this is different from ammonium, NH₄⁺)), we would likely to obtain a structure with ideal-like triangular geometry.