Chemistry 201
MOLECULAR ORBITAL THEORY
Study Guide
Basic Concepts
1. What are the limitations of (a) the Lewis electron–dot structures, (b) the Valence Bond
Theory? How does the dioxygen molecule, O2, demonstrate these limitations?
2. Valence Bond Theory is described as a localized approach to bonding while Molecular
Orbital Theory is considered a delocalized approach to bonding. Explain the salient points
that distinguish the two theories.
3. How is a molecular orbital different from an atomic orbital?
4. Differentiate the bonding, non–bonding, and the anti–bonding molecular orbitals.
5. What is the bond order? How does one calculate the bond order of a diatomic molecule?
How is the bond order related to bond strength and bond distance?
6. In terms of wave mechanics, what is the theoretical basis for the Molecular Orbital Theory?
Homonuclear and Heteronuclear Diatomic Molecules
7. What simple rule must be remembered when constructing molecular orbital diagrams?
8. Show that the aufbau order, Pauli’s exclusion principle, and Hund’s rule of maximum
multiplicity are still observed in Molecular Orbital Theory.
9. In molecules involving the elements B, C, and N, the 2p and the 2p molecular orbitals
switch places in terms of energy; i.e., the 2p orbital is filled up first. Why is this so?
10. Knowing the molecular orbital diagram for dioxygen, show how it explains the properties of
the molecule that are otherwise not accounted for by Valence Bond Theory.
11. In heteronuclear diatomic molecules, there is unequal contribution from each of the bonded
atoms.
(a) How is this reflected in the molecular orbital diagram?
(b) To which atomic orbital will the character of the bonding molecular orbital be most
similar? Explain.
(c) To which atomic orbital will the character of the anti–bonding molecular orbital be most
similar? Explain.
