1. What is the distinction between an atomic orbital (valence bond orbital) and a molecular orbital? How many electrons can a molecular orbital accommodate?
2. Sketch the bonding molecular orbital that results from the linear combination of two 1s orbitals. 
3. Sketch the antibonding molecular orbital that results from the linear combination of two 1s orbitals.
4. Is it possible for an np_x orbital on one atom to interact with an np_y orbital on another atom to produce molecular orbitals? Why or why not? Can the same be said of np_y and np_z orbitals on adjacent atoms?
5. Use a qualitative molecular orbital energy-level diagram to describe the bonding in S₂^2?. What is the bond order? How many unpaired electrons does it have?
6. If three atomic orbitals combine to form molecular orbitals, how many molecular orbitals are generated? How many molecular orbitals result from the combination of four atomic orbitals? From five?
7. Sketch a molecular orbital energy-level diagram for each ion. Based on your diagram, what is the bond order of each species?
   1. NO⁺
   2. NO^?
8. Represent the structure of ozone, O₃, according to the molecular orbital theory. Specifically what orbital(s) electrons occupy and what order bonds occur.
9. Draw a complete energy-level diagram for B₂. Determine the bond order and whether the molecule is paramagnetic or diamagnetic. Explain your rationale for the order of the molecular orbitals.
10. If all the p orbitals in the valence shells of two atoms interact, how many molecular orbitals are formed? Why is it not possible to form three ? bonding orbitals (and the corresponding antibonding orbitals) from the set of six porbitals?
11. Why is the molecular orbital approach to bonding called a delocalized approach?
12. Constructive and destructive interference of waves can be used to understand how bonding and antibonding molecular orbitals are formed from atomic orbitals. Does constructive interference of waves result in increased or decreased electron probability density between the nuclei? Is the result of constructive interference best described as a bonding molecular orbital or an antibonding molecular orbital?
13. What is the relationship between bond length and bond order? What effect do antibonding electrons have on bond length? on bond strength?
14. Sketch the four possible ways of combining two 2p orbitals on adjacent atoms which form the pi bonds. How many molecular orbitals can be formed by this combination? Be sure to indicate any nodal planes. (You may insert a picture of your sketch if you do not want to create this electronically. To create it electronically you can use Powerpoint or Paint). 
15. Sketch a molecular orbital energy-level diagram for each ion. Based on your diagram, what is the bond order of each species? (You may insert a picture of your sketch if you do not want to create this electronically. To create it electronically you can use Powerpoint or Paint).
    1. NF⁺
    2. NF

Chapter 21 Answers