Form J. Test #4 Last Name First Name Zumdahl, Chapters 8 and 9 November 23, 2004

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1 Form J Chemistry Name (please print) Test #4 Last Name First Name Zumdahl, Chapters 8 and 9 November 23, 2004 Instructions: 1. This exam consists of 27 questions. 2. No scratch paper is allowed. You may do the work in the test margins and on the backs of the test pages. 3. Mark the answers you choose on the test itself for your own information and also on the standard answer sheet you provided. Scoring will be based on the answer sheet. 4. When you finish, turn in both the test form and the answer form. The test form and your personal report will be returned to you at the next class. Write your name on both forms. 1. Place the bonds below in order of increasing polarity: H-H, H-O, H-F, H-S, H-Cl a) H-F < H-Cl < H-O < H-S < H-H b) H-S < H-F < H-H < H-Cl < H-O c) H-H < H-O < H-S < H-Cl < H-F d) H-H < H-S < H-O < H-Cl < H-F e) H-H < H-S < H-Cl < H-O < H-F 2. Which of the statements below is/are correct? I. F is larger than O 2 a) I only b) I and II c) II and III d) III only e) I, II, and III II. S 2 is larger than Mg 2+ III. Li + is larger than Be 2+

2 2 3. Place the following compounds in order of increasing magnitude of lattice energy (that is, from the least exothermic to the most exothermic lattice energy): MgO, CaO, KCl, KBr a) KBr CaO KCl MgO b) KCl KBr MgO CaO c) KCl KBr CaO MgO d) KBr KCl CaO MgO e) MgO KCl CaO KBr 4. Which of the substances below has the highest melting point? a) SCl 2 b) SO 2 c) NaCl d) NaBr e) HBr 5. The standard enthalpy of formation of H 2 O 2 (g) is -136 kj/mol. Use this information, along with the bond energies below, to estimate the bond energy of an OO bond. a) 298 kj/mol b) 129 kj/mol c) 248 kj/mol d) 148 kj/mol e) 458 kj/mol bond bond energy (kj/mol) HH 432 HO 467 O=O 495 OO??? 6. Which of the bonds below is expected to have the highest bond energy? a) SCl b) SBr c) ICl d) IBr e) II 7. In which of the molecules or ions below does the central atom violate the octet rule? I. PCl 5 II. BCl 3 III. IBr 2 IV. SeCl 4 a) I b) I and II c) I and III d) I, II, and IV e) I, II, III, and IV 8. Draw the Lewis structure of the ion PCl 4. How many lone pairs of electrons are around the central atom? a) O b) 1 c) 2 d) 3 e) 4

3 3 9. Three possible resonance structures of SO 2 are shown below: O S O O S O O S O A B C Which of the statements below is the best evaluation of these resonance structures? a) The true molecule more closely resembles structure C. b) The true molecule is a hybrid of structures A and B and does not resemble C at all. c) Structures A, B, and C all contribute equally to the resonance hybrid. (That is, the true molecule is an average of structures A, B, and C.) d) None of these structures are correct. 10. Draw the Lewis structure in which the octet rule is obeyed for the chlorate ion, ClO 3. What is the formal charge on chlorine when the octet rule is obeyed? a) -1 b) 0 c) +1 d) +2 e) In the ion SBr 3, how many lone pairs are around the central atom, and what is the approximate Br-S-Br bond angle? a) 2 lone pairs, ~90 b) 2 lone pairs, ~120 c) 4 lone pairs, ~90 d) 1 lone pair, ~109.5 e) 1 lone pair, ~ What is the molecular geometry that VSEPR predicts for the ion ICl 4? a) square planar b) tetrahedral c) trigonal pyramidal d) square pyramidal e) see-saw 13. Based upon VSEPR, which of the molecules or ions below are expected to have bond angles close to 109.5? I. PBr 3 II. SCl 4 III. CCl 4 IV. SeCl 2 a) III only b) II and III c) I, II and III d) I, III, and IV e) II, III, and IV 14. The bond angle in ozone, O 3, is closest to: a) 60 b) 90 c) d) 120 e) 180

4 15. Draw the Lewis structures of NO +, NO 2, and NO 3. Based upon a consideration of the Lewis structures, which of these should have the longest NO bond, and which should have the shortest NO bond? Longest bond Shortest bond a) NO + b) NO + c) d) NO + e) The azide anion has the formula N 3. In this ion, a nitrogen atom is the central atom, attached to two other nitrogen atoms. If each atom in this ion obeys the octet rule, what is the total number of resonance structures that can be drawn for azide? a) 0 b) 1 c) 2 d) 3 e) Place the following atoms in order of increasing electronegativity: H, O, F, S, Cl a) H < O < S < F < Cl b) H < S < Cl < O < F c) H < S < O < Cl < F d) S < Cl < H < O < F e) S < H < O < Cl < F 18. Use VSEPR to determine the geometries of the following species: SeO 2, IBr 2, SCl 2. Arrange these species in order of their bond angles, from the smallest bond angle to the largest bond angle. (If they all have the same bond angle, choose e ). a) SCl 2 < IBr 2 < SeO 2 b) SCl 2 < SeO 2 < IBr 2 c) SeO 2 < IBr 2 < SCl 2 d) IBr 2 < SCl 2 < SeO 2 e) SeO 2 = IBr 2 = SCl SO 2 has a net dipole moment. Which of the statements below best explains this property? a) SO 2 is a bent molecule with polar bonds. b) SO 2 is a linear molecule with polar bonds. c) SO 2 is a bent molecule with nonpolar bonds. d) SO 2 is a linear molecule with nonpolar bonds. e) SO 2 is a linear molecule with one polar bond and one nonpolar bond. 20. Which of the following is not a polar molecule? a) SCl 2 b) SF 4 c) CH 2 O (carbon is the central atom) d) ClF 3 e) SeO The angle between sp 3 hybrid orbitals is closest to a) 60 b) 90 c) d) 120 e) 180

5 5 22. Of the following, the central atom is sp 3 d 2 hybridized only in. a) PCl 5 b) XeF 3 c) PCl 3 d) Br 3 e) CH Draw the Lewis structure for formaldehyde, CH 2 O (carbon is the central atom). Which of the following statements is the valence bond description of the bond between carbon and oxygen in this molecule? a) A σ bond formed by the overlap of two 2s orbitals. b) Two π bonds formed by the overlap of two 2p orbitals. c) A σ bond formed by the overlap of sp 2 orbitals and a π bond formed by the overlap of 2p orbitals. d) Two π bonds formed by the overlap of sp 2 orbitals. e) A σ bond formed by the overlap of sp 3 orbitals. 24. Using molecular orbital theory, what is the bond order of the ion H 2? a) 0 b) 0.5 c) 1.0 d) 1.5 e) What is the molecular orbital electron configuration of He 2? a) (σ 1s ) 2 (σ 1s *) 2 b) (σ 1s ) 2 (σ 2s ) 2 c) (σ 1s ) 1 (σ 2s *) 1 (π 2p ) 2 d) (σ 1s ) 2 (σ 1s *) 1 (σ 2s ) 1 e) (σ 1s ) 2 (σ 2s *) Determine the molecular orbital electron configuration of the molecule B 2. What is the bond order of B 2, and is B 2 paramagnetic or diamagnetic? a) The bond order is 1; it is paramagnetic. b) The bond order is 1; it is diamagnetic. c) The bond order is 0.5; it is paramagnetic. d) The bond order is 0.5; it is diamagnetic. e) The bond order is 1.5; it is paramagnetic. 27. Counting only valence electrons, what is the molecular orbital electron configuration for C 2? a) (σ 2s ) 2 (σ 2s *) 2 (π 2p ) 4 b) (σ 2s ) 2 (σ 2s *) 2 (σ 2p ) 2 (π 2p ) 2 c) (σ 2s ) 2 (σ 2p ) 2 (π 2p ) 4 d) (σ 2s ) 4 (π 2p ) 4 e) (σ 2s ) 2 (σ 2p ) 2 (σ 2p *) 2 (σ 2s *) 2 Answer Key 1. e 6. a 11. a 16. d 21. c 26. a 2. c 7. e 12. a 17. b 22. b 27. a 3. d 8. b 13. d 18. b 23. c 4. c 9. a 14. d 19. a 24. b 5. b 10. d 15. d 20. e 25. a