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9. 1 Orbitals and Theories of Chemical Bonding 1. Which one of the statements concerning valence bond (VB) and molecular orbital (MO) bond theories is correct? a) MO theory predicts that electrons are localized between pairs of atoms. b) In VB theory, bonding electrons are delocalized over the molecule. c) MO theory accurately describes bonding in O2 and NO, VB theory does not. d) VB theory can describe molecular bonding in excited states. e) MO theory is used to accurately predict the colors of compounds. Answer: c 9. 2 Valence Bond Theory 2. Which of the following statements is/are CORRECT? . The overlap between an s orbital and a p orbital is called a pi-bond. 2. The overlap of two s orbitals in H2 is called a sigma bond. 3. HF is formed from the overlap of a hydrogen 1s orbital with a fluorine 2s orbital. a) 1 onlyb) 2 onlyc) 3 onlyd) 2 and 3e) 1, 2, and 3 Answer: b 3. Which of the following statements concerning hybrid orbitals is/are CORRECT? 1. The number of hybrid orbitals equals the number of atomic orbitals that are used to create the hybrids. 2. When atomic orbitals are hybridized, the s orbital and at least one p orbital are always hybridized. 3.
To create octahedral structures, two d orbitals must be hybridized along with the s and all three p orbitals. a) 1 onlyb) 2 onlyc) 3 onlyd) 2 and 3e) 1, 2, and 3 Answer: e 4. How many sigma (? ) bonds and pi (? ) bonds are in ethene, C2H4? a) four ? , one ? b) four ? , two ? c) five ? , one ? d) five ? , two ? e) six ? , zero ? Answer: c 5. How many sigma (? ) bonds and pi (? ) bonds are in carbon monoxide? a) three ? , zero ? b) two ? , one ? c) two ? , two ? d) one ? , two ? e) zero ? , three ? Answer: d 6. How many sigma (? ) bonds and pi (? ) bonds are in the following molecule? a) seven ? nd three ? b) seven ? and two ? c) five ? and five ? d) five ? and three ? e) five ? and two ? Answer: a 7. To form a molecule with a trigonal bipyramidal electron geometry, what set of pure atomic orbitals must be mixed? a) one s and three p b) one s, three p, and one d c) one s, three p, and two d d) two s, six p, and two d e) two s, six p, and four d Answer: b 8. What is the maximum number of hybridized orbitals formed by a fluorine atom? a) 1b) 2c) 3d) 4e) 6 Answer: d 9. What is the hybridization of either carbon atom in acetylene, C2H2? a) spb) sp2c) sp3d) sp3de) sp3d2 Answer: a 10.
What is the hybridization of the nitrogen atom in NCl3? a) spb) sp2c) sp3d) sp3de) sp3d2 Answer: c 11. What is the hybridization of the xenon atom in XeF2? a) spb) sp2c) sp3d) sp3de) sp3d2 Answer: d 12. What is the hybridization of the central nitrogen atom in nitrite ion, NO2-? a) spb) sp2c) sp3d) sp3de) sp3d2 Answer: b 13. What is the hybridization of the chlorine atom in chlorite ion, ClO2-? a) spb) sp2c) sp3d) sp3de) sp3d2 Answer: c 14. What is the hybridization of the central atom in a molecule with a square-planar molecular geometry? a) spb) sp2c) sp3d) sp3de) sp3d2 Answer: e 15.
What is the hybridization of each carbon atom in benzene, C6H6? Benzene contains a six-member carbon ring. a) spb) sp2c) sp3d) sp3de) sp3d2 Answer: b 16. For which of the following molecules does the central carbon atom have sp2 hybridization? a) Cl2COb) CHCl3c) CS2d) CH2Cl2e) HCN Answer: a 17. For which of the following molecules and ions does the central nitrogen atom have sp3 hybridization? a) NO2-b) HNO3c) NOBrd) NBr3e) HNO2 Answer: d 18. For which of the following molecules and ions does the central atom have sp hybridization: NO2+, O3, and I3-? a) NO2+ onlyb) O3 onlyc) I3- onlyd) O3 and I3-e) I3- and NO2+ Answer: a 9. What is the molecular geometry around a central atom that is sp3 hybridized and has two lone pairs of electrons? a) bent b) linear c) trigonal-planar d) trigonal-pyramidal e) trigonal-bipyramidal Answer: a 20. What is the molecular geometry around a central atom that is sp3d2 hybridized and has one lone pair of electrons? a) tetrahedral b) trigonal-bipyramidal c) square-planar d) square-pyramidal e) see-saw Answer: d 21. What is the molecular geometry around a central atom that is sp2 hybridized, has three sigma bonds, and one pi bond? a) trigonal-planar b) trigonal-pyramidal c) bent d) T-shaped e) tetrahedral Answer: a 2. What is the molecular geometry around a central atom that is sp3d hybridized and has one lone pair of eletrons? a) trigonal bipyramidal b) trigonal-pyramidal c) see-saw d) tetrahedral e) square-planar Answer: c 23. What is the hybridization of a central atom that has four sigma bonds and has no lone pairs of electrons? a) spb) sp2c) sp3d) sp3de) sp3d2 Answer: c 24. Upon heating, CaCO3 decomposes to CaO and CO2. What change in the hybridization of carbon occurs in this reaction? a) sp to sp2b) sp2 to sp3c) sp3 to spd) sp2 to spe) no change Answer: d 25. One product of the combustion of ethane, C2H6, is carbon dioxide.
What change in hybridization of the carbon occurs in this reaction? a) sp3 to sp2b) sp3 to spc) sp2 to sp3d) sp2 to sp3d2e) sp2 to sp Answer: b 26. Nitric acid, HNO3, dissociates in water to form nitrate ions and hydronium ions. What change in hybridization of the nitrogen atom occurs in this dissociation? a) sp2 to sp3b) sp2 to spc) sp3 to spd) sp to sp3e) no change Answer: e 27. Which of the following hybridized atoms is not possible? a) an sp hybridized carbon atom b) an sp2 hybridized sulfur atom c) an sp3 hybridized phosphorus atom d) an sp3d hybridized oxygen atom e) an sp3d2 hybridized xenon atom Answer: d 8. Which of the following characteristics apply to SO2? 1. polar bonds 2. nonpolar molecule 3. linear molecular shape 4. sp hybridized a) 1 onlyb) 1 and 2c) 3 and 4d) 1, 2, and 3e) 1, 2, 3, and 4 Answer: a 29. Dichloromethane, CH2Cl2, is a common organic solvent. Which of the following statements concerning dichloromethane is/are CORRECT? 1. CH2Cl2 has two isomers. For one isomer of CH2Cl2, the chlorine atoms are adjacent to each other and the molecule is polar. 2. CH2Cl2 has two isomers. For one isomer of CH2Cl2, the chlorine atoms are on opposites sides of the carbon atom and the molecule is nonpolar. 3.
The hybridization of the central carbon atom is sp3. a) 1 onlyb) 2 onlyc) 3 onlyd) 1 and 2e) 1, 2, and 3 Answer: c 30. For which of the following compounds is it possible for cis and trans isomers to exist? a) 1 onlyb) 2 onlyc) 3 only d) 1 and 2e) 1, 2, and 3 Answer: b 31. Which of the underlined atoms (C1, C2, N, and O) are sp2 hybridized? a) C1 and C2 b) C1, N, and O c) N and O d) O and C2 e) O only Answer: a 9. 3 Molecular Orbital Theory 32. All of the following statements concerning molecular orbital (MO) theory are correct EXCEPT a) the Pauli exclusion principle is obeyed. b) Hund’s rule is obeyed. ) electrons are assigned to orbitals of successively higher energy. d) a bonding molecular orbital is lower in energy than its parent atomic orbitals. e) the combination of two atomic orbitals creates only one molecular orbital. Answer: e 33. Atomic orbitals combine most effectively to form molecular orbitals when a) electrons in the orbitals have no spins. b) electrons in the orbitals have the same spin. c) the atomic orbitals are hybridized. d) the atomic orbitals have similar energies. e) p-orbitals are half-filled. Answer: d 34. A molecular orbital that decreases the electron density between two nuclei is said to be ________. ) hybridizedb) bondingc) antibondingd) pi-bondinge) nonpolar Answer: c The following molecular orbital diagram may be used for problems 35-48. For oxygen and fluorine, the ? 2p orbital should be lower in energy than the ? 2p. However, the diagram will still yield correct bond order and magnetic behavior for these molecules. |Energy | |________ |? *2p | | | | | | |________ | |________ |? 2p | | | | | | | |________ |? 2p | | | | | | |________ | |________ |? 2p | | | | | | | |________ |? 2s | | | | | | | |________ |? 2s | | | | | | | |________ |? *1s | | | | | | | |________ |? s | 35. According to molecular orbital theory, which of the following species is the most likely to exist? a) H22-b) He2c) Li22-d) Be2e) Be22- Answer: e 36. According to molecular orbital theory, which of the following species is least likely to exist? a) Be2b) F22+c) C22-d) Li2e) B22- Answer: a 37. According to molecular orbital theory, which of the following species has the highest bond order? a) F2b) F22+c) C22-d) Li2e) B22+ Answer: c 38. According to molecular orbital theory, what is the bond order of oxygen, O2? a) 1b) 3/2c) 2d) 5/2e) 3 Answer: c 39.
According to molecular orbital theory, what is the bond order of N2-? a) 1b) 3/2c) 2d) 5/2e) 3 Answer: d 40. According to molecular orbital theory, which of the following lists ranks the oxygen species in terms of increasing bond order? a) O22+ ; O22- ; O2 b) O22- ; O2 ; O22+ c) O2 ; O22+ ; O22- d) O2 ; O22- ; O22+ e) O22+ ; O2 ; O22- Answer: b 41. Consider the molecules B2, C2, N2 and O2. Which two molecules have the same bond order? a) B2 and C2b) B2 and O2c) C2 and N2d) C2 and O2e) N2 and O2 Answer: d 42. Use molecular orbital theory to predict which species is paramagnetic. ) N2b) O2c) F2d) Li2e) H2 Answer: b 43. Use molecular orbital theory to predict which ion is paramagnetic. a) F22+b) O22-c) O22+d) N22+e) B22- Answer: a 44. What is the molecular orbital configuration of F2? a) [core electrons] (? 2s)2 (? *2s)2 (? 2p)4 (? 2p)2 (? *2p)2 b) [core electrons] (? 2s)2 (? *2s)2 (? 2p)2 (? 2p)2 (? *2p)2 c) [core electrons] (? 2s)2 (? *2s)2 (? 2p)4 (? *2p)4 d) [core electrons] (? 2s)2 (? *2s)2 (? 2p)4 (? 2p)2 (? *2p)6 e) [core electrons] (? 2s)2 (? *2s)2 (? 2p)4 (? 2p)2 (? *2p)4 Answer: e 45. What is the molecular orbital configuration of N22+? a) [core electrons] (? s)2 (? *2s)2 (? 2p)4 (? 2p)2 (? *2p)2 b) [core electrons] (? 2s)2 (? *2s)2 (? 2p)4 c) [core electrons] (? 2s)2 (? *2s)2 (? 2p)2 (? 2p)2 d) [core electrons] (? 2s)4 (? *2s)4 e) [core electrons] (? 2s)2 (? *2s)2 (? 2p)4 (? 2p)2(? *2p)4 Answer: b 46. Assume that the molecular orbital energy diagram for a homonuclear diatomic molecule applies to a heteronuclear diatomic molecule. What is the molecular orbital configuration of NO? a) [core electrons] (? 2s)2 (? *2s)2 (? 2p)4 (? 2p)2 (? *2p)1 b) [core electrons] (? 2s)2 (? *2s)2 (? 2p)2 (? 2p)2 (? *2p)2 c) [core electrons] (? 2s)2 (? 2s)2 (? 2p)2 (? 2p)3 d) [core electrons] (? 2s)2 (? *2s)2 (? 2p)4 (? 2p)1 e) [core electrons] (? 2s)2 (? *2s)2 (? 2p)2 Answer: a 47. Assuming that the molecular orbital energy diagram for a homonuclear diatomic molecule applies to a heteronuclear diatomic molecule, determine which of the following species has the highest bond order. a) NO-b) OF-c) CN-d) O2e) NO Answer: c 48. Assuming that the molecular orbital energy diagram for a homonuclear diatomic molecule applies to a heteronuclear diatomic molecule, determine which of the following species is paramagnetic. a) NO+b) COc) CN-d) OF-e) NO
Answer: e 49. Which molecule will have the following valence molecular orbital level energy diagram? |? *2p | | | | |? *2p | | | | |? 2p | |[pic] | | |? 2p |[pic] | |[pic] | |? *2s | |[pic] | | |? 2s | |[pic][pic] | | a) Li2b) Be2c) B2d) C2e) N2 Answer: e 50. The following valence molecular orbital energy level diagram is appropriate for which one of the listed species? |? 2p | | | | |? *2p |[pic] | |[pic] | |? 2p | |[pic] | | |? 2p |[pic] | |[pic] | |? *2s | |[pic] | | |? 2s | |[pic][pic] | | a) B22-b) C22-c) N22-d) O22-e) F22- Answer: c 51. Which molecule will have the following valence molecular orbital energy level diagram? |? *2p | | | | |? *2p | | | | |? 2p | | | | ? 2p |[pic] | |[pic] | |? *2s | |[pic] | | |? 2s | |[pic][pic] | | a) Li2b) Be2c) B2d) C2e) F2 Answer: d 52. In the NO2- ion, each atom can be viewed as sp2 hybridized. Thus, each atom has one remaining unhybridized p orbital. How many ? 2p molecular orbitals (including both bonding and antibonding orbitals) are formed using the unhybridized p orbitals? a) 1b) 3c) 4d) 6e) 12 Answer: b 53. Benzene, C6H6, consists of a six member ring of sp2 hybridized carbon atoms. Each carbon atom has one unhybridized p orbital. How many ? p bonding, antibonding, and nonbonding molecular orbitals exist for benzene? a) Three ? 2p molecular orbitals exist; two bonding and one antibonding. b) Three ? 2p molecular orbitals exist; one bonding, one antibonding, and one nonbonding. c) Six ? 2p molecular orbitals exist; three bonding and three antibonding. d) Six ? 2p molecular orbitals exist; two bonding, two nonbonding, and two antibonding. e) Twelve ? 2p molecular orbitals exist; six bonding and six antibonding. Answer: c Short Answer Questions 54. Which theory, valence bond or molecule orbital, correctly predicts the existence of paramagnetic molecules?
Answer: molecular orbital theory 55. In valence bond theory, each sigma bond in CH4 is formed from the overlap of a hydrogen atom’s 1s orbital with a ____ hybridized orbital on the carbon atom. Answer: sp3 56. In molecular orbital theory, the bond order is defined as 1/2(the number of electrons in ________ orbitals minus the number of electrons in antibonding orbitals). Answer: bonding 57. Triiodide ion, I3-, has a trigonal-bipyramidal electron-pair geometry and a linear molecular geometry. The hybridization of the central iodine atom is ________. Answer: sp3d 58. The hybridization of the xenon atom in XeOF4 is ________.
Answer: sp3d2 59. Draw a Lewis structure of xenon trioxide. What is the hybridization of the xenon atom in this molecule? Answer: The hybridization is sp3. 60. Draw the valence molecular orbital energy level diagram for nitrogen monoxide, NO. |? *2p | |[pic] | | |? *2p | | | | |? 2p | |[pic] | | |? 2p |[pic] | |[pic] | |? *2s | |[pic] | | |? 2s | |[pic][pic] | | Answer: ———————– [pic] [pic] [pic] [pic]