9. Molecular Orbitals and      Molecular Structure   Previous PageNext Page
     Larger Diatomic Molecules

How does the MO picture of these molecules compare with the old Lewis electron-dot models? This is shown at the bottom of the fillin th table above. The number of bonds predicted is the same in bo g theories, but the descriptions of what the electrons are doing are somewhat different. From B onward, each Lewis model has at least one lone electron pair on each of the atoms. One lone pair from each atom, which contribute nothing to bonding, correspond to the self-canceling bonding and antibonding and orbitals in MO theory. Both theories say that two electron pairs make no contribution to bonding, but the Lewis model assigns one pair to each atom, whereas MO theory states that both are shared by the entire molecule. The sum of and does amount to one electron pair on each atom, so the two theories are not as different as they might seem at first.

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