9.9 The existence of compounds of the noble gases was once a great surprise and stimulated a great deal of theoret- ical work. Sketch the molecular orbital energy level diagram for XeF and deduce its ground-state electron configurations. Is XeF likely to have a shorter or longer bond than XeF*?

N2 and CN' are both isoelectronic. (i) Draw the molecular orbital diagram for N2 and CN molecules. (ii) Explain why CN is a toxic substance but N2 isn't. (iii) N2(g) is an inert gas that is suitable for a wide range of application. Would you expect N2" to be a stable diatomic species in the gaseous state? Explain your answer.

Carbon monoxide, CO, is isoelectronic to N2. (a) Draw aLewis structure for CO that satisfies the octet rule. (b) Assumethat the diagram in Figure 9.46 can be used to describethe MOs of CO. What is the predicted bond order forCO? Is this answer in accord with the Lewis structure youdrew in part (a)? (c) Experimentally, it is found that thehighest energy electrons in CO reside in a σ-type MO. Isthat observation consistent with Figure 9.46? If not, whatmodification needs to be made to the diagram? How doesthis modification relate to Figure 9.43? (d) Would you expectthe π2p MOs of CO to have equal atomic orbital contributionsfrom the C and O atoms? If not, which atom wouldhave the greater contribution?

The diagram that follows shows the highest-energy occupiedMOs of a neutral molecule CX, where element X is in thesame row of the periodic table as C. (a) Based on the numberof electrons, can you determine the identity of X? (b) Wouldthe molecule be diamagnetic or paramagnetic? (c) Considerthe p2p MOs of the molecule. Would you expect them to havea greater atomic orbital contribution from C, have a greateratomic orbital contribution from X, or be an equal mixtureof atomic orbitals from the two atoms?