Chemical Engineering Chapter 11 1 Explain what is meant by the term “bond order” and describe how it can be calculated using the information in a molecular orbital energy level diagram

Chapter 11: Theories of Covalent Bonding

1. According to valence bond theory, which orbitals on N and H overlap in the NH3

molecule?

A) 2p on N overlaps with 2s on H D) sp3 on N overlaps with sp on H

B) 2p on N overlaps with 1s on H E) sp3 on N overlaps with 1s on H

C) 2s on N overlaps with 1s on H

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

A) sp hybrid orbitals D) sp3d hybrid orbitals

B) sp2 hybrid orbitals E) sp3d2 hybrid orbitals

C) sp3 hybrid orbitals

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

A) sp hybrid orbitals D) sp3d hybrid orbitals

B) sp2 hybrid orbitals E) sp3d2 hybrid orbitals

C) sp3 hybrid orbitals

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

A) sp hybrid orbitals D) sp3d hybrid orbitals

B) sp2 hybrid orbitals E) sp3d2 hybrid orbitals

C) sp3 hybrid orbitals

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

A) s and p atomic orbitals D) sp hybrid orbitals

B) sp3 hybrid orbitals E) sp3d2 hybrid orbitals

C) sp2 hybrid orbitals

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

A) sp2 hybrid orbitals D) sp3d2 hybrid orbitals

B) sp3 hybrid orbitals E) none of the above

C) sp3d hybrid orbitals

Chapter 11: Theories of Covalent Bonding

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

A) sp hybrid orbitals D) sp3d hybrid orbitals

B) sp2 hybrid orbitals E) sp3d2 hybrid orbitals

C) sp3 hybrid orbitals

8. Carbon uses ______ hybrid orbitals in ClCN.

A) sp B) sp2 C) sp3 D) sp3d E) sp3d2

9. Valence bond theory predicts that carbon will use _____ hybrid orbitals in the carbonate

anion, CO32–.

A) sp B) sp2 C) sp3 D) sp3d E) sp3d2

10. Valence bond theory predicts that sulfur will use _____ hybrid orbitals in sulfur dioxide,

SO2.

A) sp B) sp2 C) sp3 D) sp3d E) sp3d2

11. When PCl5 solidifies it forms PCl4+ cations and PCl6– anions. According to valence bond

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

A) sp B) sp2 C) sp3 D) sp3d E) sp3d2

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

A) sp B) sp2 C) sp3 D) sp3d E) sp3d2

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

A) sp2 B) sp3 C) sp3d D) sp3d 2 E) d2sp3

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

A) sp2 B) sp3 C) sp3d D) sp3d 2 E) none of the above

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

A) sp2 B) sp3 C) sp3d D) sp3d 2 E) none of the above

16. Valence bond theory predicts that bromine will use _____ hybrid orbitals in BrF3.

A) sp2 B) sp3 C) sp3d D) sp4 E) sp3d2

Chapter 11: Theories of Covalent Bonding

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

A) sp B) sp2 C) sp3 D) sp3d E) sp3d2

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

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.

19. For which one of the following molecules is the indicated type of hybridization not

appropriate for the central atom?

A) BeCl2 sp2 D) C2H2 sp

B) SiH4 sp3 E) H2O sp3

C) BF3 sp2

20. According to valence bond theory, which of the following molecules involves sp2

hybridization of orbitals on the central atom? (central atom is bold)

A) C2H2 B) C2H4 C) C2H6 D) CO2 E) H2O

21. Determine the shape (geometry) of PCl3 and then decide on the appropriate hybridization

of phosphorus in this molecule. (Phosphorus is the central atom.)

A) sp3 B) sp2 C) sp D) sp3d E) sp3d 2

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

A) three  bonds and no  bonds. D) no  bonds and three  bonds.

B) two  bonds and one  bond. E) none of the above.

C) one  bond and two  bonds.

23. How many sigma and pi bonds, respectively, are in the molecule below?

CH3CH2CHCHCH3?

A) 16, 1 B) 16, 0 C) 15, 1 D) 15, 0 E) 14, 1

Chapter 11: Theories of Covalent Bonding

24. Select the correct statement about -bonds in valence bond theory.

A) A  bond is stronger than a sigma bond.

B) A  bond can hold 4 electrons, two above and two below the -bond axis.

C) A carbon-carbon double bond consists of two  bonds.

D) A  bond is the same strength as a  bond.

E) A  bond between two carbon atoms restricts rotation about the C–C axis.

25. According to molecular orbital (MO) theory, the twelve outermost electrons in the O2

molecule are 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.

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

A) 5.5 B) 5 C) 4 D) 2.5 E) 1.5

27. According to the molecular orbital (MO) treatment of the NO molecule, what are the

bond order and the number of unpaired electrons, respectively?

A) 2, 2 B) 3, 3 C) 1, 1 D) 1.5, 2 E) 2.5, 1

28. Which of the following statements relating to molecular orbital (MO) theory is

incorrect?

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.

29. One can safely assume that the 3s– and 3p-orbitals will form molecular orbitals similar to

those formed when 2s– and 2p-orbitals interact. According to molecular orbital theory, what will

be the bond order for the Cl2+ ion?

A) 0.5 B) 1 C) 1.5 D) 2 E) none of the above

Chapter 11: Theories of Covalent Bonding

30. The nitrosonium ion, NO+, forms a number of interesting complexes with nickel, cobalt,

and iron. According 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.

31. Which one, if any, of the following statements about the MO treatment of the bonding in

benzene is correct?

A) MO theory uses resonance to describe the delocalized nature of the bonding in

benzene.

B) The lowest energy pi-bonding orbital in benzene can hold up to 6 electrons.

C) MO theory predicts that benzene should be paramagnetic.

D) The lowest energy pi-bonding MO in benzene has two hexagonal lobes, above and

below the plane of the carbon atoms.

E) None of the above statements is correct.

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

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

of hybridization.

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

Chapter 11: Theories of Covalent Bonding

35. Describe the bonding in ethylene (ethene, C2H4) according to valence bond theory. Be

sure to 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.

36. a. In the context of valence bond theory, explain the difference in geometry between a 

and a  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?

37. In one sentence state how molecular orbitals are usually obtained.

38. Sketch the shapes of the 1s and 1s* molecular orbitals formed by the overlap of two

hydrogen 1s atomic orbitals.

Chapter 11: Theories of Covalent Bonding

39. Explain what is meant by a node (or nodal plane) in a molecular orbital and draw

sketches of the following orbitals, indicating at least one nodal plane in each one.

a. a * orbital

b. a * orbital

40. In the context of molecular orbital (MO) theory, explain how atomic p orbitals can give

rise to:

a. a  MO

b. a  MO

41. Explain what is meant by the term “bond order” and describe how it can be calculated

using the information in a molecular orbital energy level diagram.

42. a. What simple experiment could you perform to show that a substance is paramagnetic?

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.

Chapter 11: Theories of Covalent Bonding

43. According to valence bond theory, overlap of bonding orbitals of atoms will weaken a

bond, due to electron-electron repulsion.

44. Valence bond theory explains the bonding in diatomic molecules such as HCl without

resorting to the use of hybrid orbitals.

45. Hybrid orbitals of the sp3d type occur in sets of four.

46. The angles between sp2 hybrid orbitals are 109.5°.

47. Atoms of period 3 and beyond can undergo sp3d 2 hybridization, but atoms of period 2

cannot.

48. In the valence bond treatment, overlap of an s orbital on one atom with an sp3 orbital on

another atom can give rise to a  bond.

49. Overlap of two sp2 hybrid orbitals produces a  bond.

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

side.

51. A carbon-carbon double bond in a molecule may give rise to the existence of cis and

trans isomers.

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

isomers.

53. Valence bond theory is able to explain why molecular oxygen is paramagnetic.

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

orbitals.

Chapter 11: Theories of Covalent Bonding

55. In applying molecular orbital theory, the bond order is calculated in the same way as

with Lewis structures.

56. In molecular orbital theory, molecules with an even number of electrons will have bond

orders which are whole numbers.

57. In molecular orbital theory, combination of two 2p atomic orbitals may give rise to either

 or  type molecular orbitals.

58. According to molecular orbital theory, all diatomic molecules with an even number of

electrons will be diamagnetic.