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e2f10 - Version PREVIEW Exam 1 JOHNSON(53140 This print-out...

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Version PREVIEW – Exam 1 – JOHNSON – (53140) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. LDE Identifying Bonds 005 001 10.0 points Rank the labeled bonds in the molecule below from least to most polar. C c b N H e O H a S d S H 1. c < e < b < a < c 2. c < d < e < a < b 3. d < c < e < b < a correct 4. c < d < e < b < a 5. d < c < b < e < a Explanation: Bonds a, b, c, d, and e have a ΔEN of 1.4, 1.0, 0.5, 0.0, and 0.9, respectively. Brodbelt 013 322 002 10.0 points Which of the following statements about po- larity is false? 1. Linear molecules can be polar. 2. Polar molecules must have a net dipole moment. 3. Lone (unshared) pairs of electrons on the central atom play an important role in influ- encing polarity. 4. CCl 4 is a polar molecule. correct 5. Dipole moments can “cancel”, giving a net non-polar molecule. 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. ChemPrin3e T03 39 003 10.0 points Which of the following is NOT polar? 1. COCl 2 2. ClF 3 3. BrO 3 4. CH + 3 correct 5. O 3 Explanation: COCl 2 (the central atom is C) is polar be- cause there are two different bonds: C=O and C-Cl which have different sized dipoles so their effects do not cancel. The other in- correct choices have either 3, 4 or 5 RHED: one or more of these are lone pairs on the central atom which causes the polar bonds to be placed in positions where the dipole of at least one bond is not opposing another, caus- ing the species to be polar. In CH + 3 there are no lone pairs; the C-H bonds are at 120 so their effects cancel and the ion is nonpolar. ChemPrin3e T03 22 004 10.0 points Which of the following has bond angles slightly less than 109 ? 1. NH + 4 2. BrO 3 correct
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Version PREVIEW – Exam 1 – JOHNSON – (53140) 2 3. ClO 4 4. BH 4 5. PO 3 4 Explanation: While all structures have four regions of electron density around the central atom, only BrO 3 also has one of these regions as a lone pair. Since the lone pair requires more room, the other bonds are repelled away from it slightly, folding them up rather like an um- brella and resulting in angles slightly less than 109.5 . Brodbelt 013 320 005 10.0 points The sp 3 hybridization has what percent s character and what percent p character? 1. 50%; 50% 2. 33%; 67% 3. 67%; 33% 4. 75%; 25% 5. 25%; 75% correct Explanation: s = 1 4 = 25% p = 3 4 = 75% Brodbelt 013 308 006 10.0 points NF 2 has (2, 3, 4) regions of high electron density and (2, 4, 6) bonded electrons. 1. 2; 2 2. 4; 4 correct 3. 2; 4 4. 4; 6 5. 2; 6 6. 4; 2 7. 3; 4 8. 3; 6 9. 3; 2 Explanation: N = 8 × 3 = 25 A = 5 + (7 × 2) + 1 = 20 S = 24 - 20 = 4 First, draw the molecule. The number of regions of HED equals the number of bonds and the number of lone pairs. There are 4 shared, or bonded electrons, giving 2 regions of HED. The 2 F atoms have an octet. This means that 16 of the 20 available electrons are
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