Lecture 12 Hybridization of Atomic Orbitals

Lecture 12 Hybridization of Atomic Orbitals - Hybridization...

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Hybridization of Atomic Orbitals B. A. Rowland 53750/53760 Hybridization Overview Experimental studies (basically, spectroscopy) shows that the four single bonds in the molecule methane (CH 4 ) are exactly identical: they have the same length as well as the same energy—there is no bond that is longer/shorter or stronger/weaker than the others. We would like to begin to analyze what atomic orbitals are used by the molecule to make its single, double, and triple bonds. We can begin our analysis with atomic orbitals. Using methane as an example, we know carbon has a valence of 4 electrons (1s 2 2s 2 2p 2 ). It would appear that one electron in each of the four shared bonds in methane comes from these. There are two problems with this reasoning, however. First, remember that the 2s orbital is lower in energy than the 2p orbital. This would result in 2 bonds in methane (2s) having lower energy than the other 2 bonds (2p). This clearly violates the experimental results! Also, we know that the molecular geometry of methane is tetrahedral. An examination of the shapes of the 2s and 2p orbitals shows that the 2s orbital is a spherical shape centered around the nucleus (conceivably no problem) but that the 3 suborbitals of the 2p orbital lie along the x-, y-, and z- axes (and not at the tips of a tetrahedral)! The atomic orbitals do not have the correct geometry to ensure a tetrahedral structure. We remedy this situation by introducing hybrid orbitals (mixtures of atomic orbitals). By taking the raw atomic orbitals we can use a mathematical prescription to take some weighted linear combination of the s, p, and even d orbitals to generate an equivalent number of lobes of a hybrid orbital. By adjusting the parameters in the weighting correctly, we can ensure that each sub lobe of the hybrid orbital will have exactly the same energy AND the correct geometry for the steric number of interest. Remember: the number of atomic orbitals used to make the hybrid = the number of lobes
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This note was uploaded on 02/02/2009 for the course CH 53750 taught by Professor Rowland during the Spring '09 term at University of Texas at Austin.

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Lecture 12 Hybridization of Atomic Orbitals - Hybridization...

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