14. How do the observed bond lengths and bond energies of the second-row diatomic molecules correlate with the predicted bond order?

15. When AO's of different kinds of atoms are being combined to build an MO, what important energy criterion helps to decide which AO's on the two atoms will interact9 What symmetry considerations are important? Illustrate with the HF molecule.

16. Draw the Lewis electron-dot model for the HF molecule. The F atom should be represented as having one bond to H, and three lone electron pairs. In MO theory, what orbitals do these three electron pairs occupy? Which fluorine AO is involved in the H-F bond?

17. To which MO does the fluorine 2p AO make the greatest contribution, the bonding MO or the antibonding? What does this imply in terms of the location of the bonding electron pair and the polarity of the bond? How is this related to the relative electronegativities of H and F?

18. How are the energy levels of the hydrogen is and fluorine 2p atomic orbitals related to the first ionization energies of H and F? (The correlation is approximate, but useful.)

19. In the limit of completely ionic bonding between two atoms of very high and very low electronegativities, how would the bonding MO compare with the AO's of the two atoms? What would this . I Illustrate imply about the location of the bonding electron pair. with NaCl.