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CH_301-Sutcliffe-Exam2

CH_301-Sutcliffe-Exam2 - Version 102 Exam 2 T Th...

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Version 102 – Exam 2 T Th – sutcliffe – (50985) 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 10.0 points Hint: ’Lowest’ means ’least negative’. If the following crystallize in the same type of structure, which has the lowest lattice en- ergy? 1. CaO 2. SrS 3. BaS correct 4. BaO 5. SrO Explanation: Lowest charge densities due to larger size. 002 10.0 points Assume in this question the octet rule is strictly obeyed. The Lewis dot structure of BrO + 3 has how many total electrons and how many shared electrons? 1. 24; 6 2. 25; 6 3. 26; 6 4. 25; 8 5. 24; 8 correct 6. 26; 8 7. 26; 7 8. 25; 7 Explanation: The total number of valence electrons is 1 × 7 e (for Br) + 3 × 6 e (for O) - 1 e (from + 1 charge) = 24 e Br is the central atom, with the O atoms ar- ranged around it. Br 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: Br O O O + 003 10.0 points In this question assume the octet rule is strictly obeyed. Which of the following exhibits resonance? 1. ClO 3 2. O 2 3. NO 3 correct 4. H 3 O + Explanation: The structure for the NO 3 ion is N · · · · · · O · · · · · · O · · · · O This is a resonance structure because the double bond could be placed at any of the O atoms. 004 10.0 points The molecular formula for phosgene is COCl 2 , with carbon being the central atom. The elec- tronic arrangement is ? and the molecular shape is ? . 1. trigonal planar; angular 2. tetrahedral; tetrahedral 3. trigonal bipyramidal; T-shaped 4. trigonal planar; trigonal planar correct 5. tetrahedral; trigonal planar
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Version 102 – Exam 2 T Th – sutcliffe – (50985) 2 Explanation: 005 10.0 points The approximate F-P-F bond angle in the PF + 4 ion is 1. 90 /120 . 2. 90 . 3. 120 . 4. 109.5 . correct 5. 60 . Explanation: For PF + 4 , S = N - A = 40 - 32 = 8 e = 4 bonds and 8 / 2 / 4 = 1 = single bonds only. A structure with sp 3 tetrahedral electronic and molecular geometry with 4 P F bonds would satisfy the octet rule and result in a total of 32 valence electrons. The angles are therefore all 109.5 . 006 10.0 points Which of the following has bond angles of 90 , 120 , and 180 ? 1. IF 5 2. PF 6 3. XeF 4 4. ICl 4 5. SF 4 correct Explanation: Only SF 4 has five regions of electron density around the central atom; the rest have six. 007 10.0 points The dot structure for BeCl 2 has how many lone pairs on the central atom? 1. 3 2. 0 correct 3. 2 4. 1 5. 5 6. 4 Explanation: Beryllium brings in 2 valence electrons and each chlorine brings in 7 valence electrons, for a total of 16 valence electrons: Cl Be Cl and the octet rule is satisfied for each Cl. Be is a known exception to the octet rule in that it can form stable compounds with only 4 valence electrons.
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