Exam 2 October 29, time finished. Notes on exam format:

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1 Chemistry Inorganic Chemistry Exam 2 October 29, 2001 GROUND RULES: a. Closed book; closed notes; no consulting b. allowed: calculator; model set; point group flowchart; ruler c. 180 minute (3 h) time limit d. Due Saturday v. 3, 5:00 p.m. e. please fill in and sign: time started time finished I have abided by the ground rules in taking this exam: tes on exam format: This exam consists of 7 short questions and 3 long questions

2 Short Answer Section a. The enthalpies of reaction of trimethylboron with N 3, C 3 N 2, (C 3 ) 2 N and (C 3 ) 3 N are -58, -74, -81, and -74 kj/mol respectively. Briefly explain the likely reason why trimethylamine is out of line. b. (i) Br and I are equivalently strong acids in water due to solvent leveling. Explain. (ii) What is a solvent in which the relative strengths of Br and I could be determined? (Show, using a chemical equation.) c. In terms of hard-soft acid-base theory, which end of the SCN - anion would coordinate to: (a) Cr 3+ (b) Pt 2+ Briefly explain your choices. 2

3 d. Which of each pair is the stronger acid in water? For each case, briefly explain why? (i) Sn 4 (ii) ClO (iii) [Ru( 2 O) 6 ] 2+ For part (iii), give a chemical equation that shows how the ion you chose acts as an acid. e. Show equations for how the following compounds react when placed in water. (int: each one makes a solution with p>7.) (i) Na (ii) N 3 f. Using the principles of SAB theory, determine whether K eq > 1 or K eq < 1 for the following reaction. Briefly explain. Cl 3 Al PEt 3 + Cl 3 In NMe 3 Cl 3 Al NMe 3 + Cl 3 In PEt 3 3

4 g. Using Drago-Wayland E, C parameters, determine which of Et 3 N, Et 2 O and PMe 3 is the stronger base toward GaMe 3. 4

5 Longer questions 1. Consider the following series of six platinum compounds. number molecular formula # of ions 1 PtCl 2 4N PtCl 2 3N PtCl 2 2N PtCl 2 2N KPtCl 3 N K 2 PtCl 4 3 From the molecular formulas and numbers of ions produced when each compound is dissolved in water, deduce the structural formula of each compound, being explicit as to which ligands are in the coordination sphere. Draw structures for each platinum containing molecule or ion. te that compounds 3 and 4 are isomers (one is polar, one is non-polar). All of the compounds have the same geometry at platinum what is that geometry? 5

6 2. (a) Draw a molecular orbital diagram for 2. (b) Label the orbitals with the proper symmetry label (σ or π) and label any non-bonding and antibonding orbitals. (c) What is the point group of 2? (d) Sketch the atomic and molecular orbitals as part of your diagram. (e) Using the MO diagram for 2, interact two 2 fragments to make tetrahedral 4. You should consider tetrahedral 4 to be formed by the approach of 2 2 fragments perpendicular to one another as shown in the drawings below. Arrange your coordinate system as you like. approach at 90 angle tetrahedral 4 (f) Label the MO s of 4 in order of increasing energy φ 1, φ 2, φ 3, φ 4. (g) Sketch the shape of these four MO's. (h) ow many nodes does each orbital have? (i) Are any of the orbitals degenerate in energy? If so, which ones? (j) What is the point group of tetrahedral 4? 6

7 3. Give a clear well-labeled molecular orbital diagram for the Cl molecule. Pay attention to the relative energies of the orbitals used to make the diagram. Valence orbital energy levels are given at the end of the exam. Include pictures of all orbitals (atomic and molecular). 7

8 Useful information: Selected E and C parameters for the Drago E,C equation: - (kj/mol) = E A E B + C A C B acid E A (kj/mol) 1/2 C A base E B (kj/mol) 1/2 (kj/mol) 1/2 C B (kj/mol) 1/2 BMe py AlMe N AlEt Me 3 N GaMe Et 3 N GaEt Me 2 O InMe Et 2 O SbCl TF BF Me 2 S Et 2 S Me 3 P Me 2 Se

9 Valence orbital potential energies: Orbital potential energy (ev) Atomic Element 1s 2s 2p 3s 3p Number e Li Be B C N O F Ne Na Mg Al Si P S Cl Ar

10 linear? Group of low symmetry? (lacking any C n?) σh? Group of high symmetry? ( 2 C nw/ n>2 for each) D h C v C 1, C i, C s ighest order rotation axis (n)? Td, Oh, Ih C n Are there n C 2 s? D n groups C n or S 2n groups σ h? σ h? D nh σ d? C nh σ v? D nd D n C nv S 2n? S 2n C n 10