Boron diatomic molecule, orbitals

Of these three diatomic moiecuies, only N2 exists under normal conditions. Boron and carbon form soiid networks rather than isolated diatomic molecules. However, molecular orbital theory predicts that B2 and C2 are stable molecules under the right conditions, and in fact both molecules can be generated in the gas phase by vaporizing solid boron or soiid carbon in the form of graphite. 

FIGURE 6.19 Correlation diagram for heteronuclear diatomic molecules, AB. The atomic orbitals for the more electronegative atom (B) are displaced downward because they have lower energies than those for A. The orbital filling shown is that for (boron monoxide) BO. 

The bond order in N2, O2, and F2 is the same whether or not mixing is taken into account, but the order of the (Tg(2p) and TT (2p) orbitals is different in N2 than in O2 and F2. As stated previously and further described in Section 5.3.1, the energy difference between the 2s and 2p orbitals of the second row main group elements increases with increasing Z, from 5.7 eV in boron to 21.5 eV in fluorine. As this difference increases, the s-p interaction (mixing) decreases, and the normal order of molecular orbitals returns in O2 and F2. The higher a-g(2p) orbital (relative to 7T (2p)) occurs in many heteronuclear diatomic molecules, such as CO, described in Section 5.3.1. 

Given the energy ordering of the molecular orbitals, it is a simple matter to determine the electron configurations for the second-row diatomic molecules B2 through Ne2. For example, a boron atom has three valence electrons. (Remember that we need to consider the inner-shell Is electrons.) Thus, for B2 we must place six electrons in MOs. Four of these fully occupy the (T2s and molecular... 

Write an orbital wave function without antisymmetrization or normalization for the diatomic boron molecule in its ground level. 

Describe the bonding in the boron nitride (BN) molecule using both the molecular orbital method and the valence-bond method. Compare the BN molecule with diatomic carbon. 

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