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Unformatted text preview: 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 – find all choices before answering. The due time is Central time. Each question is worth as assigned. 001 (part 1 of 1) 6 points Use VSEPR theory to predict the molecular geometry of the molecule HCN. 1. trigonal-pyramidal 2. trigonal-bipyramidal 3. octahedral 4. None of these 5. trigonal-planar 6. tetrahedral 7. linear correct 8. bent or angular Explanation: molecular geometry of HCN = ? The Lewis structure for HCN is H C ¡ ¡ ¢ ¢ N £ £ ¤ ¤ or C N ¥ ¥ H Although there is an octet of electrons around C, six electrons are combined to form a triple bond. The two areas of high elec- tron density around the central atom make the molecular geometry linear. 002 (part 1 of 1) 6 points Choose the incorrect formula from the follow- 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 of each I- , so the formula for lithium iodide is LiI. The barium ion is Ba 2+ ; the fluoride ion is F- . Two F- are needed to balance the charge of each Ba 2+ , so the formula is BaF 2 . The sodium ion is Na + ; the chloride ion is Cl- . One Cl- is needed to balance the charge of each Na + , so the formula is NaCl. The calcium ion is Ca 2+ ; sulfide ion is S 2- . One S 2- is needed to balance the charge of each Ca 2+ , so the formula is CaS. The compound formed from aluminum and chlorine is a covalent compound. We check that a stable dot structure can be drawn for AlCl 3 . Al has 3 valence electrons and each Cl has 7 valence electrons, so there are a total of 24 valence electrons available for 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 of valence electrons (24). This would be the most likely formula for the compound formed from Al and Cl. 003 (part 1 of 1) 4 points The Lewis dot structure for an isolated silicon atom has 1. two pairs of electrons. 2. one pair of electrons and three lone elec- trons. 3. one pair of electrons and two lone elec- trons. correct 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....
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This note was uploaded on 01/30/2010 for the course CH 301 taught by Professor Fakhreddine/lyon during the Spring '07 term at University of Texas at Austin.
- Spring '07