2009 Exam 4 Key

2009 Exam 4 Key - Name Section Number Chemistry 1314 Honors...

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N a m e Section Number Chemistry 1314 Honors Midterm Exam #4 December 7, 2009 This exam is closed book, notes, papers, etc. You may use a calculator. If you need a physical constant or unit conversion factor that is not provided, please ask. This exam must represent your own work. Note: R=8.314 J/mol K = 0.0821 L atm/mol K Scores: 1. / 20 2. a. / 7 b. / 7 c. / 6 3. a. / 7 b. / 6 c. / 7 4. a. / 6 b. / 8 c. / 6 5. a. / 8 b. / 6 c. / 6 Total: / 100
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CHEM 1314 H Midterm Exam #4, 2009 Page 2 1. For each of the following molecules: (i) Draw a Lewis structure. (ii) Calculate formal charges on all atoms to prove that your structure is reasonable. (iii) Using VSEPR theory, sketch and name the approximate geometry of the molecule and describe any distortions you predict away from this approximate geometry. (iv) Describe the hybridization of the central atom(s) in each molecule. 1 point for each part for each of items i through iv. a. SiH 4 b. SeO 3 Lewis Structure Ideal tetrahedral geometry (Bond angles = 109.5º) Si H H H H Si H H H H All formal charges = 0 sp 3 hybridization c. I 3 - Lewis Structure Ideal trigonal planar (Bond angles = 120º) Se O O O Se O O O All formal charges = 0 sp 2 hybridization d. SF 4 Lewis Structure Linear (Bond angle = 180º) II - I - I Inner I formal charge = -1 Outer Is = 0 sp 3 d hybridization e. H 2 C 2 Lewis Structure See-saw (Bond angles = see below) S F F F F All formal charges = 0 sp 3 d hybridization Lewis Structure Linear (Bond angles = 180º) CC H H H H All formal charges = 0 sp hybridization
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CHEM 1314 H Midterm Exam #4, 2009 Page 3 2. In terms of the relevant intermolecular forces , explain each of the following experimental observations about the boiling points for the hydrides given in the figure to the right. a. Within a specific group , the boiling point of the hydride of the period 3 element is always less than the boiling point of the hydride of the period 4 element, which in turn is always less than the boiling point of the hydride of the period 5 elements. b. Within a given period , the hydride of the group 4 element always has the lowest boiling point (Note: Be sure to explain why the factors from part (a) aren’t relevant here).
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2009 Exam 4 Key - Name Section Number Chemistry 1314 Honors...

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