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Unformatted text preview: Version 352 Exam 2 mccord (51600) 1 This print-out should have 35 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 3.0 points The Lewis dot structure of CO 2 3 has how many total electrons and how many shared electrons? 1. 24; 8 correct 2. 32; 10 3. 32; 8 4. 32; 6 5. 24; 6 6. 24; 10 Explanation: The total number of valence electrons is 1 4 e (for C) + 3 6 e (for O) +2 e (from- 2 charge) = 24 e C is the central atom, with the O atoms arranged around it. C will have an incomplete octet if we show one shared pair of electrons (a single bond) with each O, so one double bond is necessary: C O b b b b b b O b b b b b b O b b b b 002 3.0 points Which of the following species is/are param- agnetic? I) Li 2 II) O 2 III) H + 2 1. III only 2. I and II 3. I, II and III correct 4. I only 5. I and III 6. II and III 7. II only Explanation: Li 2 and H + 2 both have an odd number of electrons and therefore must be paramag- netic. O 2 has 16 total electrons, the last two of which must go into separate degenerate anti-bonding orbitals. 003 3.0 points The MO diagram in this problem is for a homonuclear diatomic molecule from the 2nd row of the periodic table. Consider the following molecular orbital di- agram: a b c What are the names of the labeled orbitals, a , b , and c , respectively? 1. 2 p , 2 p , 1 s 2. 2 p , 2 p , 2 s 3. 2 p , 2 p , 2 s 4. 2 p , 2 p , 2 s correct 5. 2 p , 2 p , 2 s Explanation: 004 2.0 points Which of the following compounds has an ionic bond? 1. SO 3 Version 352 Exam 2 mccord (51600) 2 2. CO 2 3. HCl 4. NaCl correct Explanation: Ionic bonds form when two elements re- act that have very different electronegativ- ity values. Generally this occurs when met- als (low electronegativity) and non-metals (higher electronegativity) react with each other. Sodium chloride (NaCl) is composed of a metal and non-metal and would have an ionic bond. 005 3.0 points Rank the following atoms and ions Li + , Be 2+ , He , H , B 3+ in order of decreasing size. 1. B 3+ , Be 2+ , He, Li + , H 2. He, H , Li + , Be 2+ , B 3+ 3. B 3+ , Be 2+ , Li + , He, H 4. H , He, Li + , Be 2+ , B 3+ correct 5. H , Li + , He, Be 2+ , B 3+ Explanation: We are comparing ions with the same num- ber of electrons (that have noble gas con- figurations): 2 total and 2 valence in this case. The number of protons in the ion is the biggest determinate of the size when electron number is constant. Since there are no in- ner shell electrons to shield the nucleus, the effective nuclear charge is just the charge of the nucleus. The greater the effective nuclear charge, the stronger the attraction between the protons and the electrons, and thus the smaller the radii....
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- Spring '08