# Does the hybridization model gives us any further insight on Molecular Geometry?

It doesn't seem as though the hybridization model adds anything useful to the discussion of molecular geometry as predicted by the VSEPR model. It's just another way of labeling linear, trigonal planar, and tetrahedral geometry (as $sp$, $sp^2$, and $sp^3$, respectively). Considering that orbital hybridization may not be the most accurate view of molecular bonding, what is the utility of having it around?

VSEPR, however, is a predictive tool, although it has no significant quantum mechanical basis. The VSEPR model is based upon the idea that pairs of electrons (whether bonding or not) will repel one another. Geometrical factors are considered to determine how far away pairs of electrons can be from one another (e.g 180 degrees apart for two pairs, and 120 degrees apart for 3 pairs). The model accurately predicts the H-C-H angle in methane and also predicts that the H-N-H angle in ammonia is closer to 109 degrees than 120 (as is the case in a molecule such as $BF_3$. Because VSEPR assumes ideal conditions, the model starts to fall apart when considering complex molecules. For example, while the VSEPR model correctly predicts that $SF_4$ is seesaw shaped, it can only predict that the structure won't be precisely seesaw (with F-S-F angles of 180, 120 and 90 degrees). It only allows us to suggest that the lone pair on the sulfur will be a "space hog" in a manner of speaking and repel the bonding electrons.
Now, on to the last part of your question why do we still use it? (This is somewhat speculative and opinion-based.) We have to blame the organic chemists here. orbital hybridization terminology ($sp^2, sp^3$, ...) provides a lexicon for describing the bonding environments of carbon atoms that is compact and visually constructive for organic molecules. If I state that there is an $sp^2$ carbon in a molecule, you can begin to visualize what that part of the molecule looks like, that it is a region of planarity, that it cannot be a chiral center, that it likely has a double bond and therefore may undergo certain types of chemical reactions, etc. So while orbital hybridization doesn't provide any insight into molecular geometry, it provides a basis for terminology that chemists can use to transmit meaningful information.
• @GregE. Consider an atom of carbon. With MO theory, the same 1 2s and 3 2p orbitals are engaging in bonding regardless of whether the ultimate structure contains a single or double bond; however, in the hybridization model, we must first look at the result and then say, "Oh, because there is a double bond, we must have had $sp^2$ orbitals. Once we can assign a "hybridization", we can make some predictions about the chemistry, I agree. – bobthechemist Dec 29 '13 at 13:44