Chem2070-P2Key - CHEMISTRY 2070 PRELIM II November 12, 2009...

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CHEMISTRY 2070 PRELIM II November 12, 2009 ANSWER KEY Your Name: ( Please print ) Last First CORNELL NetID Day and Time of Your Lab-Recitation Section: Lab-Recitation TA: Complete academic integrity is expected of all students of Cornell University at all times, whether in the presence or absence of members of the faculty or teaching staF. Understanding this, I declare that I shall not give, use, or receive unauthorized aid in this examination. Your Signature: There are 6 (multipart) questions and a total of 12 pages (including this cover sheet, a blank page after all the questions and a periodic table at the end). Make sure that your examination booklet is complete. The prelim is not designed with the idea that all, or necessarily any of you, will complete each and every question. Write your answers directly on these sheets. Use the blank page, or if necessary the backs of pages, but clearly indicate on the problem page where work can be found. If you need to include additional pages, please attach them securely to the rest of the test book. Be brief, concise, and neat. Include only material pertinent to the question asked. Proctors are not allowed to interpret questions for you. In case of doubt, indicate the assumptions on which your answer is based. No additional formulas, or values of fundamental constants, are required to answer these questions; if you believe that there is missing information, please check to make sure that you have taken advantage of any information provided to you in the problem. You may leave when you are Fnished, except in the Fnal minutes of the exam. Please do so quietly after turning your paper. Question 1. (32) Question 2. (28) Question 3. (24) Question 4. (28) Question 5. (30) Question 6. (33) Total (175) Show your work! (Unless you don’t care to receive partial credit). 1
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1. (32 points) (a) Below is shown the molecule known as acrylonitrile. The 3 carbon atoms are identifed in the drawing where all bonds have been identifed. i. (6 points) Add lone pair/individual electrons to the diagram above so that all valence electrons From all atoms are shown. How many valence electrons are Found in your completed structure? One lone pair belongs on the N atom. There are: 2 valence electrons in lone pairs, plus two more bonding electrons in each of the 9 bonds; for a total of 20. Or, 5 in N, 4 in each of 3 C atoms, and 1 in each of 3 H atoms, for a total of 20. ii. (6 points) IdentiFy the hybridization schemes at each oF the 3 carbon atoms. Carbon #1: Carbon #2: Carbon #3: sp sp 2 sp 2 iii. (5 points) How many σ bonds are Found in the structure as drawn? σ bonds are the “Frst bonds” formed; one between each bound pair of atoms. So there is one C-N σ bond, 2 C-C σ bonds, and 3 C-H σ bonds. ±or a total of 6. iv. (5 points) How many π bonds are Found in the structure as drawn?
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Chem2070-P2Key - CHEMISTRY 2070 PRELIM II November 12, 2009...

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