Chem 400. Inorganic Chemistry. Exam 1. Σ of of of of of of of of 10. Name (please print)

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1 Chem 400 Inorganic Chemistr Eam 1 1 of 10 2 of 10 3 of 30 4 of 10 5 of 10 6 of 20 7 of 10 Σ of 100 % Name (please print)

2 1. Sketch out the molecular orbital energ level diagram for B 3 appling the LGO approach. Define the spatial orientation of B 3 using,,z directions and identif all atomic and ligand group orbitals involved in bonding. (10 points) Planar B 3 ψ 7 node z 2p z 2p 2p ψ 5 ψ 4 ψ 6 LGO(3) LGO(2) LGO(1) LGO(2) LGO(3) Energ ψ 2 ψ 3 LGO(1) 2s B ψ 1 B B 3 All atoms of B 3 lie in the plane, coincides with principal rotation ais. LGO s of 3 fragment are derived b taking linear combinations of the three 1 s orbitals. 1

3 2. Draw schematic representations for all of the bonding and antibonding molecular orbitals (MO s) of B 3 (use the information derived in Problem 1). (10 points) ψ 1 ψ 2 ψ 3 ψ 4 p z ψ 7 ψ 5 ψ 6 2

4 3. Draw Lewis structures for each of the following molecules. (2 points each) Based on our Lewis structure, develop threedimensional structures for each compound using VSEPR theor. (2 points each) inall, determine the appropriate point group for each of our three dimensional drawings. (2 points each) a. Br 4 Br Br D 4h b. I 7 I I D 5h c. SiClBrI Cl Cl Si I Br Si I Br C 1 d. S 5 S S C 4v 3

5 e. 2 O 2 O O O O C 2h 4. ow man normal modes of vibration does each of the following molecules possess, and how man of those are IR active for (2 points each): a. CCl 4 CCl 4 is tetrahedral and nonpolar; T d smmetr. our modes of vibrational freedom are IR active and give rise to two bands in the IR. b. BCl 3 BCl 3 has a trigonal planar structure and is nonpolar. Therefore, the smmetric stretch is IR inactive. ive modes of vibrational freedom give rise to three bands in the IR spectrum. c. CS 2 CS 2 is linear and nonpolar. Thus the asmteric stretch and the doubl degenerate deformation are IR active, giving rise to two bands in the IR spectrum. d. 2 S 2 S is polar and possesses a bent molecular shape. All three modes of vibration are IR active. e. N 3 N 3 has trigonal pramidal structure and is polar. There are si modes of vibrational freedom giving rise to four bands in the IR spectrum. 4

6 6 5. Give the epected possible covalent MX n compounds ( where X = Cl or Br ) of Sn, At, and Ra. Assume onl σbonding, and predict the geometr of each molecule. int: To predict possible covalent states, start with the ground state electron configurations of the atom and obtain the simplest possible covalent state b utilizing onl the initiall unpaired electrons in covalent bond formation. The partial table below indicates would tpe of answer I epect. (10 points) Valence State Configuration bridization ormula Geometr Sn sp 2 SnX 2 sp 3 SnX 4 bent tetrahedral At sp 3 AtX linear sp 3 d sp 3 d 2 AtX 3 AtX 5 Tshaped square pramidal sp 3 d 3 AtX 5 pentagonal bipramidal Ra sd RaX 2 bent

7 6.a Draw an MO energlevel diagram for the MOs that would arise in a diatomic molecule from the combination of unhbridized d orbitals. Label the AOs being combined and the resulting MOs. Let the z ais lie along the σbond. (10 points) σ* π 1 * π 2 * Energ δ 1 * δ 2 * d 2 2 d 2 2 d d d d z z d z d z d d z 2 z 2 Note: dorbitals are degenerate, drawn at different energies to simplif figure. δ 1 δ 2 π 1 π 2 σ AO M MO MM AO M b. Sketch the shape of the resulting MO s. (10 points) σ π 1 z z π 2 δ 1 d z 2 d z 2 d z d z d z d z d 2 2 d 2 2 δ 2 π 1 * z π 2 * z δ 1 * d d d z d z d z d z d 2 2 d 2 2 δ 2 * σ* d d d z 2 d z 2 6

8 8 7. Assign (1) formal charges, (2) oidation numbers, and (3) evaluate the relative importance of the three Lewis structures of OCN, the canate ion. Compare these (i.e., do the same) to the Lewis structures of the fulminate ion, CNO. (10 points) or canate ion: a) O C N b) O C N c) O C N ormal charges Oidation numbers II IV III II IV III II IV III Best charge distribution is in b). Structure b) should be the most important, with structure a) net. Structure c) should be unimportant because of poor charge distribution. or fulminate ion: a) O N C b) O N C c) O N C ormal charges Oidation numbers II IV 0 II I II II III I The best structure is b), the second best a). Structure c) should be unimportant because of poor charge distribution. Etra Credit: Eplain the observation that the canate ion is stable, the fulminate ion is eplosive, and CON does not eist. (2 points) The poor charge distribution in the fulminate ion is the source of its eplosiveness.