Molecular Orbitals of Other Diatomic Molecules

The approximate wavefunction for H2 is similar to that for the He atom in that there are now two electrons that need spatial functions, and the overall spin-orbital wavefunction must be antisymmetric with respect to exchange of the two electrons. Recall that the wavefunction for the electron in the bonding orbital of H2, from equation 12.43, is 

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The other wavefunction from equation 12.43 is for the antibonding orbital. Because both electrons can be described with this spatial wavefunction, the spatial wave-function for the H2 molecule is the product of two such 

Because both electrons reside in the a bonding orbital, an electron configuration of can be used to describe the ground electronic state of H2. (Because H2 is a homonuclear diatomic molecule, we add a subscript g to the label——to indicate the orbital s symmetry property with respect to the center of the molecule. Electrons in the antibonding orbital are labeled a, the u also referring to the orbital s symmetry properties. Symmetry will be discussed in the next chapter.) To emphasize that the electrons in the a orbital derive from Is electrons from H atoms, the more detailed (cTgls) label can also be used. 

Larger atoms have more occupied atomic orbitals that can combine into molecular orbitals. It is common to use the second row of atoms, Li through Ne, to illustrate the principles. For diatomics having electrons originating from different atomic electronic shells, we adopt the approximation that only atomic orbitals of similar energies will combine to make molecular orbitals. 

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