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Exam 2-solutions - Version 298 Exam 2 mccord(50970 This...

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Version 298 – Exam 2 – mccord – (50970) 1 This print-out should have 34 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. McCord CH301 001 10.0 points Consider the following pairs A and B A 1 ) N N O A 2 ) N N O B 1 ) P O O O O 3 B 2 ) P O O O O 3 of Lewis structures. Select the one from each pair that is likely to make the dominant contribution to a reso- nance hybrid. 1. A 2 and B 2 2. A 1 and B 1 3. A 1 and B 2 4. A 2 and B 1 correct Explanation: A 1 ) N N O - 1 +1 0 A 2 ) N N O 0 +1 - 1 The second structure is preferred because it places the negative formal charge on the most electronegative atom. B 1 ) P O O O O 0 - 1 - 1 - 1 0 3 B 2 ) P O O O O 0 0 - 1 - 1 - 1 3 The first structure is preferred for the same reason. 002 10.0 points The electronic arrangment is the same as the molecular shape when 1. there are no lone pairs of electrons on the central atom. correct 2. there are more shared electrons than non- shared electrons. 3. the molecule is not polar. 4. the number of bonding orbitals equals the number of anti-bonding orbitals. 5. the atoms are joined by sigma bonds. Explanation: The only time that the molecular shape and electronic arrangement are the same is when there are no lone pairs of electrons on the central atom. 003 10.0 points Which of the following would have the highest melting point? 1. KF correct 2. KI 3. KBr 4. KCl 5. RbF Explanation: KF has the highest charge density. 004 10.0 points The energy diagram in this question is the molecular orbital diagram for a homonuclear diatomic molecule. The lines represent MO’s but the labels have been removed. Consider the following molecular orbital di- agram:
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Version 298 – Exam 2 – mccord – (50970) 2 a b c What are the names of the labeled orbitals, a through c, respectively? 1. π 2 p 2 p 1 s 2. σ 2 p 2 p 1 s 3. π 2 p 2 p 1 s correct 4. π 2 p 2 p 2 s 5. σ 2 p 2 p 2 s Explanation: 005 0.0 points EXTRA CREDIT QUESTION: A re- minder here to PLEASE bubble in your name, uteid, and your version number correctly. Do it now - don’t wait till the end of the exam. Also, a reminder that there is NO CLASS tomorrow (Friday, October 8th). That’s right, you get to SKIP chemistry class. I’ll see you on Monday, the 11th, and we’ll start up on Chapter 5. This question starts out at zero points but could very well increase after the grad- ing. Now, if more points are awarded (the curve) on this assignment, would you like them added to your score? 1. NO, leave my score alone, I prefer the lower score 2. YES, I would like the points and the higher score. correct Explanation: This should be a no-brainer. Most students want higher scores. If you picked yes, you got credit for the question and you got the extra points you asked for (if they were granted by your instructor). If you answered NO, you also got what you wanted... no points awarded.
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