Chem 1 Exam 2 - Panjwani, Sameer Test 2 Due: Jul 12 2007,...

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Panjwani, Sameer – Test 2 – Due: Jul 12 2007, 4:00 pm – Inst: Fakhreddine/Lyon 1 This print-out should have 35 questions. Multiple-choice questions may continue on the next column or page – fnd all choices be±ore answering. The due time is Central time. Each question is worth as assigned. 001 (part 1 o± 1) 6 points UseVSEPRtheorytopredictthemolecular geometry o± the molecule HCN. 1. trigonal-pyramidal 2. trigonal-bipyramidal 3. octahedral 4. None o± these 5. trigonal-planar 6. tetrahedral 7. linear correct 8. bent or angular Explanation: molecular geometry o± HCN = ? The Lewis structure ±or HCN is H C N or C N H Although there is an octet o± electrons around C, six electrons are combined to ±orm a triple bond. The two areas o± high elec- tron density around the central atom make the molecular geometry linear. 002 (part 1 o± 1) 6 points Choose the incorrect ±ormula ±rom the ±ollow- ing. 1. BaF 2 2. NaBr 3. Li 2 I correct 4. AlCl 3 5. CaS Explanation: The lithium ion is Li + ; the iodine is I - . One Li + is needed to balance the charge o± each I - , so the ±ormula ±or lithium iodide is LiI. The barium ion is Ba 2+ ; the ²uoride ion is F - . Two F - are needed to balance the charge o± each Ba 2+ , so the ±ormula is BaF 2 . The sodium ion is Na + ; the chloride ion is Cl - . One Cl - is needed to balance the charge o± each Na + , so the ±ormula is NaCl. The calcium ion is Ca 2+ ; sulfde ion is S 2 - . One S 2 - is needed to balance the charge o± each Ca 2+ , so the ±ormula is CaS. The compound ±ormed ±rom aluminum and chlorine is a covalent compound. We check that a stable dot structure can be drawn ±or AlCl 3 . Al has 3 valence electrons and each Cl has 7 valence electrons, so there are a total o± 24 valence electrons available ±or the structure. Aluminum, like boron above it, can be an exception to the octet rule and there could be only six electrons around Al in our structure: Al · · · · · · Cl · · · ·· · Cl · · · · ·· Cl This structure shows a complete octet around each Cl and six electrons around Al. The structure has the correct total number o± valence electrons (24). This would be the most likely ±ormula ±or the compound ±ormed ±rom Al and Cl. 003 (part 1 o± 1) 4 points The Lewis dot structure ±or an isolated silicon atom has 1. two pairs o± electrons. 2. one pair o± electrons and three lone elec- trons. 3. one pair o± electrons and two lone elec- trons. correct
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Panjwani, Sameer – Test 2 – Due: Jul 12 2007, 4:00 pm – Inst: Fakhreddine/Lyon 2 4. four lone electrons. 5. three pairs of electrons. Explanation: 004 (part 1 of 1) 6 points Rank the following atoms and ions Li + , Be 2+ , He , H - , B 3+ in order of decreasing size. 1.
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This note was uploaded on 03/18/2008 for the course CH 301 taught by Professor Fakhreddine/lyon during the Summer '07 term at University of Texas at Austin.

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Chem 1 Exam 2 - Panjwani, Sameer Test 2 Due: Jul 12 2007,...

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