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Unformatted text preview: nanni (arn437) HW 08 VSEPR vanden bout (50985) 1 This print-out should have 31 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Which of the following statements about po- larity is false? 1. Linear molecules can be polar. 2. Lone (unshared) pairs of electrons on the central atom play an important role in influ- encing polarity. 3. Dipole moments can cancel, giving a net non-polar molecule. 4. Polar molecules must have a net dipole moment. 5. CCl 4 is a polar molecule. correct Explanation: The Lewis Dot structure for CCl 4 is C Cl Cl Cl Cl The molecule has tetrahedral electronic and molecular geometry. The C- Cl bond is polar, but becuase of the symmetry of the molecule, the individual dipole moments cancel. The molecule is therefore nonpolar. 002 10.0 points Which of the following molecules is nonpolar? 1. NF 3 2. SO 2 3. BF 3 correct 4. H 2 O 5. CH 3 Br Explanation: The structure for BF 3 is B F F F There are no lone pairs on B. This is a symmetrical molecule and non-polar. 003 10.0 points CHF 3 is (less,more) polar than CHI 3 because 1. more; the C-F bonds are more polar than the C-I bonds. correct 2. less; the C-H bond in CHF 3 is a non-polar bond. 3. less; the three polar C-F bonds are sym- metrical and cancel the dipole moments. 4. more; the C-H bond in CHF 3 is a non- polar bond. 5. less; the tetrahedral geometry decreases the polarity of C-F bonds. Explanation: Since F is more electronegative than I, a C-F bond will have a greater difference in electronegativities than a C-I bond. 004 10.0 points Which of the molecules I) O b b b b H H II) Cl b b b b b b Cl b b b b b b III) B Cl b b b b b b Cl b b b b b b Cl b b b b b b contains polar covalent bonds but is NOT itself a polar molecule? 1. None fit the criteria. nanni (arn437) HW 08 VSEPR vanden bout (50985) 2 2. All fit the criteria. 3. II and III only 4. II only 5. I only 6. I and II only 7. III only correct 8. I and III only Explanation: I) Water has polar covalent bonds and is itself polar. II) Chlorine gas has nonpolar bonds only. III) Boron trichloride contains polar covalent bonds but is not polar overall due to symmetry. 005 10.0 points Consider a 3-atom molecule A B A for which B has a total of only four valence elec- trons enough to make two bonds. Predict the A-B-A bond angle. 1. 60 2. 90 3. 180 correct 4. 109.5 5. 120 Explanation: 006 10.0 points What is the shape of COCl 2 ? 1. tetrahedral 2. T-shaped 3. trigonal pyramidal 4. seesaw 5. trigonal planar correct Explanation: There are three regions of electron density (with no lone pairs) around the central atom: C Cl b b b b b b Cl b b b b b b O b b b b 007 10.0 points Which of the following has bond angles slightly LESS than 120 ?...
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- Fall '10