Test 2 - Version 372 Exam 2 McCord(53130 This print-out...

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Version 372 – Exam 2 – McCord – (53130) 1 This print-out should have 31 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. McCord CH301tt This exam is only for McCord’s Tues/Thur CH301 class. If Quest works properly, you should be able to see your score for this exam by 11:30 PM tonight. Do realize however that Quest has been taking up to 8 hours to get through the grading, so your score might appear bit by bit. I will post an announcement on our web page and/or Quest when I feel like all bubblesheets have been graded. PLEASE carefully bubble in your UTEID and Version Number! We av- erage about 20-30 students per exam that misbubble this information. Get it right! 001 10.0 points The molecule AX 3 is polar and obeys the octet rule; therefore, the central atom A 1. has one lone pair of electrons. correct 2. has four lone pairs of electrons. 3. has no lone pairs of electrons. 4. has two lone pairs of electrons. 5. has three lone pairs of electrons. Explanation: The molecule AX 3 could obey the octet rule in one of two ways. The molecule could contain two A - X single bonds and one A - X double bond, yielding the structure A X X X This molecule would have a trigonal planar geometry. It is symmetrical and therefore non-polar, so this is not the correct structure for our molecule. The second possible dot structure for AX 3 is A ·· X X X This molecule obeys the octet rule and has a pyramidal molecular geometry. Assuming there is an electronegativity difference be- tween A and X, this molecule would be polar. This structure has one lone pair on A. 002 10.0 points After constructing the Lewis dot formula for CCl 3 , give its electronic arrangement and molecular shape. 1. tetrahedral, angular 2. trigonal bipyramidal, seesaw 3. tetrahedral, tetrahedral 4. trigonal bipyramidal, T-shaped 5. tetrahedral, trigonal pyramidal correct 6. trigonal planar, trigonal planar Explanation: N = 8(4) = 32 A = 1 + 4 + 3(7) = 26 S = 32 - 26 = 6 003 10.0 points Which of the following has bond angles slightly less than 109.5 ? 1. COCl 2 2. AsF 3 correct 3. COS 4. SO 2
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Version 372 – Exam 2 – McCord – (53130) 2 5. CS 2 3 Explanation: AsF 3 has four regions of electron density, one of which is a lone pair, which repels the other regions, making those bond angles less than 109.5 . 004 10.0 points Which of the following ions has a tetrahe- dral molecular (actual) geometry? 1. NO 3 2. H 3 O + 3. CO 2 3 4. H 2 F + 5. NH + 4 correct Explanation: N H H H H For the central atom N, HED = 4 and lone pairs = 0, so the electronic and molecular geometries are also tetrahedral. N H H H H 005 10.0 points How many non-bonding electron pairs are on the central atom in SF 5 ? 1. 3 2. 1 correct 3. 4 4. 0 5. 2 Explanation: The total number of valence electrons is S 1 × 6 e = 6 e F 5 × 7 e = 35 e - 1 charge +1 e = 1 e 42 e and S F F F F F is the Lewis struc- ture.
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