Theories of Covalent BondingChapter 11

Multiple Choice Questions

1. A molecule with the formula AX2 uses _________ to form its bonds.E

a. sp hybrid orbitalsb. sp2 hybrid orbitalsc. sp3 hybrid orbitalsd. sp3d hybrid orbitalse. sp3d2 hybrid orbitals

2. A molecule with the formula AX3 uses __________ to form its bonds.E

a. sp hybrid orbitalsb. sp2 hybrid orbitalsc. sp3 hybrid orbitalsd. sp3d hybrid orbitalse. sp3d2 hybrid orbitals

3. A molecule with the formula AX4 uses _________ to form its bonds.E

a. sp hybrid orbitalsb. sp2 hybrid orbitalsc. sp3 hybrid orbitalsd. sp3d hybrid orbitalse. sp3d2 hybrid orbitals

4. A molecule with the formula AX3E uses _________ to form its bonds.M

a. s and p atomic orbitalsb. sp3 hybrid orbitalsc. sp2 hybrid orbitalsd. sp hybrid orbitalse. sp3d2 hybrid orbitals

5. A molecule with the formula AX4E uses _________ to form its bonds.M

a. sp2 hybrid orbitalsb. sp3 hybrid orbitalsc. sp3d hybrid orbitalsd. sp3d2 hybrid orbitalse. none of the above

6. A molecule with the formula AX4E2 uses _________ to form its bonds.M

a. sp hybrid orbitalsb. sp2 hybrid orbitalsc. sp3 hybrid orbitalsd. sp3d hybrid orbitalse. sp3d2 hybrid orbitals

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7. Carbon uses ______ hybrid orbitals in ClCN.M

a. spb. sp2

c. sp3

d. sp3de. sp3d2

8. Valence bond theory predicts that carbon will use _____ hybrid orbitals in the carbonate anion, CO32–.

Ma. spb. sp2

c. sp3

d. sp3de. sp3d2

9. Valence bond theory predicts that sulfur will use _____ hybrid orbitals in sulfur dioxide, SO2.M

a. spb. sp2

c. sp3

d. sp3de. sp3d2

10. When PCl5 solidifies it forms PCl4+ cations and PCl6

– anions. According to valence bond theory,

M what hybrid orbitals are used by phosphorus in the PCl4+ cations?

a. spb. sp2

c. sp3

d. sp3de. sp3d2

11. Valence bond theory predicts that tin will use _____ hybrid orbitals in SnCl3–.

Ma. spb. sp2

c. sp3

d. sp3de. sp3d2

12. Valence bond theory predicts that tin will use _____ hybrid orbitals in SnF5–.

Ma. sp2

b. sp3

c. sp3dd. sp3d 2

e. sp3d2

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13. Valence bond theory predicts that iodine will use _____ hybrid orbitals in ICl2–.

Ma. sp2

b. sp3

c. sp3dd. sp3d 2

e. none of the above

14. Valence bond theory predicts that bromine will use _____ hybrid orbitals in BrF5.M

a. sp2

b. sp3

c. sp3dd. sp3d 2

e. none of the above

15. Valence bond theory predicts that xenon will use _____ hybrid orbitals in XeOF4.M

a. spb. sp2

c. sp3

d. sp3de. sp3d 2

16. Which one of the following statements about orbital hybridization is incorrect?M

a. The carbon atom in CH4 is sp3 hybridized.b. The carbon atom in CO2 is sp hybridized.c. The nitrogen atom in NH3 is sp2 hybridized.d. sp2 hybrid orbitals are coplanar, and at 120 to each other.e. sp hybrid orbitals lie at 180 to each other.

17. For which one of the following molecules is the indicated type of hybridization not appropriate for M the central atom?

a. BeCl2 sp2

b. SiH4 sp3

c. BF3 sp2

d. C2H2 spe. H2O sp3

18. According to valence bond theory, which of the following molecules involves sp2 hybridization of M orbitals on the central atom? (central atom is bold)

a. C2H2

b. C2H4

c. C2H6

d. CO2

e. H2O

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19. Determine the shape (geometry) of PCl3 and then decide on the appropriate hybridization of M phosphorus in this molecule. (Phosphorus is the central atom.)

a. sp3 b. sp2

c. spd. sp3de. sp3d 2

20. According to valence bond theory, the triple bond in ethyne (acetylene, C2H2) consists of E

a. three bonds and no bonds.b. two bonds and one bond.c. one bond and two bonds.d. no bonds and three bonds.e. none of the above.

21. According to molecular orbital (MO) theory, the twelve outermost electrons in the O2 molecule are H distributed as follows:

a. 12 in bonding MOs, 0 in antibonding MOs.b. 10 in bonding MOs, 2 in antibonding MOs.c. 9 in bonding MOs, 3 in antibonding MOs.d. 8 in bonding MOs, 4 in antibonding MOs.e. 7 in bonding MOs, 5 in antibonding MOs.

22. According to molecular orbital theory, what is the bond order in the O2+ ion?

Ha. 5.5b. 5c. 4d. 2.5e. 1.5

23. Which of the following statements relating to molecular orbital (MO) theory is incorrect?M

a. Combination of two atomic orbitals produces one bonding and one antibonding MO.b. A bonding MO is lower in energy than the two atomic orbitals from which it is formed.c. Combination of two 2p orbitals may result in either or MOs.d. A species with a bond order of zero will not be stable.e. In a stable molecule having an even number of electrons, all electrons must be paired.

24. One can safely assume that the 3s- and 3p-orbitals will form molecular orbitals similar to those formed when H 2s- and 2p-orbitals interact. According to molecular orbital theory, what will be the bond order for the

Cl2+ ion?

a. 0.5b. 1c. 1.5d. 2e. none of the above

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25. The nitrosonium ion, NO+, forms a number of interesting complexes with nickel, cobalt, and iron. According H to molecular orbital theory, which of the following statements about NO+ is correct?

a. NO+ has a bond order of 2 and is paramagnetic.b. NO+ has a bond order of 2 and is diamagnetic.c. NO+ has a bond order of 3 and is paramagnetic.d. NO+ has a bond order of 3 and is diamagnetic.e. None of the above statements is correct.

Short Answer Questions

26. In one sentence state the basic principle of valence bond theory.M

27. In not more than two sentences, explain when and why chemists make use of the concept of hybridization.M

28. What type of hybridization is needed to explain why ethyne, C2H2, is linear?E

29. Describe the bonding in ethylene (ethene, C2H4) according to valence bond theory. Be sure to H indicate the orbital hybridization on the carbon atoms. Draw a diagram clearly showing at least one bond of

each type which occurs in the molecule.

30. a. In the context of valence bond theory, explain the difference in geometry between a and a H bond. Use a real molecule to illustrate your answer.

b. What two important differences are there in the properties of and bonds, in terms of how they affect the structure and reactivity of molecules?

31. In one sentence state how molecular orbitals are usually obtained.M

32. Sketch the shapes of the 1s and 1s* molecular orbitals formed by the overlap of two hydrogen 1s M atomic orbitals.

33. Explain what is meant by a node (or nodal plane) in a molecular orbital and draw sketches of the M following orbitals, indicating at least one nodal plane in each one.

a. a * orbitalb. a * orbital

34. In the context of molecular orbital (MO) theory, explain how atomic p orbitals can give rise to:M a. a MO

b. a MO

35. Explain what is meant by the term “bond order” and describe how it can be calculated using the M information in a molecular orbital energy level diagram.

36. a. What simple experiment could you perform to show that a substance is paramagnetic? M b. What microscopic (atomic/molecular) feature must a substance possess in order to be paramagnetic?

c. Can it be predicted whether or not all homonuclear diatomic ions, X2+, will be paramagnetic? Explain.

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True/False Questions

37. According to valence bond theory, overlap of bonding orbitals of atoms will weaken a bond, due H to electron-electron repulsion.

38. Valence bond theory explains the bonding in diatomic molecules such as HCl without resorting to E the use of hybrid orbitals.

39. Hybrid orbitals of the sp3d type occur in sets of four.E

40. The angles between sp2 hybrid orbitals are 109.5.E

41. Atoms of period 3 and beyond can undergo sp3d 2 hybridization, but atoms of period 2 cannot.M

42. In the valence bond treatment, overlap of an s orbital on one atom with an sp3 orbital on another E atom can give rise to a bond.

43. Overlap of two sp2 hybrid orbitals produces a bond.M

44. In the valence bond treatment, a bond is formed when two 2p orbitals overlap side to side.M

45. A carbon-carbon double bond in a molecule may give rise to the existence of cis and trans isomers.M

46. A carbon-carbon triple bond in a molecule may give rise to the existence of cis and trans isomers.M

47. In molecular orbital theory, combination of two atomic orbitals produces two molecular orbitals.E

48. In applying molecular orbital theory, the bond order is calculated in the same way as with M Lewis structures.

49. In molecular orbital theory, molecules with an even number of electrons will have bond orders M which are whole numbers.

50. In molecular orbital theory, combination of two 2p atomic orbitals may give rise to either or M type molecular orbitals.

51. According to molecular orbital theory, all diatomic molecules with an even number of electrons M will be diamagnetic.

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Theories of Covalent BondingChapter 11

Answer Key

1. a2. b3. c4. b5. c6. e7. a8. b9. b

10. c11. c12. c13. c14. d15. e16. c17. a18. b

19. a20. c21. d22. d23. e24. c25. d

26. A covalent bond forms when the orbitals of two atoms overlap and a pair of electrons occupies the region between the nuclei.

27. Chemists postulate hybridization when the observed geometry of a molecule cannot be rationalized in terms of overlap of the s, p and/or d orbitals of the atoms concerned.

28. sp

29. The carbon atoms are sp2 hybridized, leaving the 2pz orbital on each carbon unhybridized. Overlap of one sp2 hybrid on each carbon and occupation of this region by an electron pair produces a C–C bond. Overlap of the remaining four hybrid orbitals with 1s orbitals of four hydrogen atoms, produces four C–H bonds. The unhybridized 2pz orbitals overlap laterally to produce a bond which has two regions of electron density, above and below the C–C bond. (Diagram needed.)

30. a. A bond has its region of highest electron density between the bonded atoms, along the axis joining them. A bond has two regions of overlap, between the atoms but above and below the axis joining them.

b. A bond is stronger than a bond. There is free rotation about a bond but not about a bond, giving rise to the possibility of geometrical isomers in the latter case.

31. By the linear combination (addition or subtraction) of atomic orbitals.

32.

1s 1s*

33. A nodal plane is a plane of zero electron density. Nodal planes are the dashed lines shown below.

a. b.

34. a. A MO arises when atomic p orbitals which are directed towards each other, are combined.b. A MO arises from the combination of atomic p orbitals which lie parallel to each other, perpendicular to the internuclear axis.

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35. The bond order in MO theory is the net number of bonds, where a pair of electrons in a bonding MO constitutes a bond and a pair in an antibonding MO constitutes an antibond. It is equal to the total number of electrons in bonding MOs minus the total number in antibonding MOs, divided by two.

36. a. Place a sample of the substance near a magnet; if it is attracted to the magnet, it is paramagnetic.b. The substance must have unpaired electrons in order to be paramagnetic.c. Yes, they will necessarily be paramagnetic since each will have an odd number of electrons.

37. F

38. T

39. F

40. F

41. T

42. T

43. F

44. T

45. T

46. F

47. T

48. F

49. T

50. T

51. F

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