1. When atomic orbitals are combined into molecular orbitals, how does the number of MO's obtained compare with the original number of AO's?

2. For a multiatorn molecule, what approximation are we using when we combine atomic orbitals from atoms two at a time in forming bonds between pairs of atoms? Why is this approximation useful? Give an example of a molecule for which this approximation is valid, and another for which it breaks down.

3. What is the distinction between bonding and antibonding MO's? How is it that molecules such as N and F can have antibonding orbitals that are lower in energy than some bonding orbitals?

4. How many electrons can each MO hold? What is the relationship between the spins of electrons occupying the same MO? How does this compare with the occupancy of AO's by electrons in isolated atoms?

5. In the hydrogenlike diatomic molecules , H, , and He, why do the first two electrons increase the strength of the bond, and the third and fourth electrons weaken the bond? What is the bond order in each of the above molecules or molecule-ions?

6. Compare the theoretical predictions in Question 5 with the observed bond lengths and bond energies. Does the bond length increase, or decrease, with increasing bond order? Why?

7. How do filled bonding MO's tend to hold the two bonded atomic nuclei together? How do filled antibonding MO's tend to pull them apart? Explain in terms of electron probability distributions.

8. What are the requirements in terms of location, energy, and symmetry of two atomic orbitals if they are to be combined into molecular orbitals?