CHM 501


Final Exam 1999

All references are to articles from J. Am. Chem. Soc., 1999, 121.

1. P. Ghigna, G. Spinola, U. Anselmi-Tamburini, F. Maglia, M. Dapiaggi, G. Spina, and L. Cianchi (p. 301-309) studied cubic zirconia, ZrO2, doped with about 10% iron. Cubic zirconia has the fluorite structure. Estimate the lattice energy using the Born-Landé equation. Calculate the experimental lattice energy using a Born-Haber cycle (the sublimation energy of Zr is 608.8 kJ/mole, the heat of formation of ZrO2 is -1100.6 kJ/mol, and EA2 for oxygen is -779.6 kJ/mol). Compare the experimental and theoretical estimates. The iron-doped species were found to have most of the Fe in the +2 oxidation state. Give the formula of the nonstochiometric compound. Would you expect the Fe-doped material to be a semiconductor? Why or why not? If so, is it an n-type or p-type semiconductor? The authors found the distance between iron and zirconium nuclei to be 264 pm; they claim that this is evidence of a metal-metal bond. Evaluate this claim. (Metallic radii: Fe, 126 pm; Zr, 160 pm; covalent radii: Fe, 120 pm; Zr, 148 pm; ionic radii are in your textbook.)
electron configuration
n
[He]
5
[Ne]
7
[Ar]
9
[Kr]
10
[Xe]
12

2. E. Y. Misochko, A. V. Akimov, I. U. Goldschleger, A. I. Boldyrev, and C. A. Wight (p. 405-410) investigated F2NO. Write two low energy Lewis dot structures, predict the molecular geometry including estimates of all bond angles, and give the point group. What is the hybridization about the nitrogen atom?

3. A. Irigoras, J. E. Fowler, J. M. Ugalde (p. 574-580) looked at the reactions of Sc+ in the 3D and 1D states in water. They claim these are two low-lying electronic states; do you concur? Why or why not? Find all of the Russell-Saunders states.

4. T. M. Barclay, A. W. Cordes, R. C. Haddon, M. E. Itkis, R. T. Oakley, R. W. Reed, and H. Zhang (p. 969-976) found that the radical shown below is an electrical conductor in the solid state. Complete the Lewis structure shown below. The compound forms slipped-stacks, as depicted. Which orbitals form the valence and conduction bands? What is the degree of filling of each of these bands?


5. A. Ranganathan, V. R. Pedireddi, and C. N. R. Rao (p. 1752-1753) cocrystallized a 1:1 mixture of melamine (M) and cyanuric acid (CA), which gave a solid state structure of hexagons known as a rosette as shown below. Each M and CA are held together by three interactions. Show one M-CA structure, identify the three interactions, and estimate the relative strengths of each of these interactions. Defend your reasoning.


6. M. C. Holthausen, W. Koch, and Y. Apeloig (p. 2623-2624) considered the properties of silylenes, SiR2. The issue that concerned the authors was whether the ground state was a singlet or a triplet. Triplets can occur if the HOMO and LUMO are close enough in energy so that spin pairing costs more energy than singly occupying a higher energy orbital. Use group theoretical methods to construct an MO diagram for SiH2, showing sketches of all of the group orbitals. What is the bond order?

7. J. Ren, C. J. Cramer, and R. R. Squires (p. 2623-2624) used Lewis acid-base properties to estimate the Bronsted/Lowry acid strength of some carbonyl compounds. In one experiment, they reacted BF3 with acetone. Write the reaction, draw the structure of the product, and estimate the heat of reaction. For BF3, E = 20.2, C = 3.31; CH3COCH3, E = 2.02, C = 4.67; units give kJ/mol.