Chapter 8

91. Which of the following species has the shortest carbon−nitrogen bond?

CH3CN

44. When both of the electrons in a molecular bond originate from the same atom, the bond is called a(n)

coordinate covalent bond.

90. Using the following data reactions: ΔH° (kJ/mol-rxn) H2(g) + Cl2(g) → 2HCl(g) -184 H2(g) → 2H(g) 432 Cl2(g) → 2Cl(g) 239 calculate the energy of an H-Cl bond.

d. 428 kJ/mol

14. If two or more species have the same number of electrons, resulting in similar Lewis structures, they are said to be ____.

isoelectronic

63. Use VSEPR theory to predict the molecular geometry around either carbon atom in acetylene, C2H2.

linear

43. Which of the following elements is most likely to form a molecular structure that disobeys the octet rule?

B

32. What is the formal charge on the carbon atom in CO?

0

51. Which of the following species has a Lewis structure similar to iodine tetrafluoride, IF4-?

XeF4

10. How many lone pairs of electrons are assigned to the carbon atom in CO?

3

42. Which of the following elements is able to form a molecular structure that exceeds the octet rule?

Cl

61. Use VSEPR theory to predict the electron-pair geometry and the molecular geometry of xenon tetrafluoride, XeF4.

The electron-pair geometry is octahedral, the molecular geometry is square-planar.

56. What is the molecular geometry around the nitrogen atom as per the valence shell electron-pair repulsion (VSEPR) theory??

Trigonal pyramidal

80. Which of the following molecules is nonpolar?

phosphorus trifluoride, PF3

50. The central atom in SF6 is surrounded by

six single bonds and no lone pairs of electrons.

7. An atom of He has _____ valence electrons.

2

73. Which of the following bonds would be the most polar?

N--Ga

25. Which of the following Lewis structures for nitrogen oxides is incorrect?

N2O3.

15. Which of the following has a Lewis structure similar to OCS?

N2O^+

72. Place the following molecules in order from smallest to largest H−N−H bond angles: NH4+, NH3, and NH2-.

NH2^- < NH3 < NH4^+

6. Which of the following statements is/are CORRECT? 1. Chemical reactions result in the gain, loss, or rearrangement of valence electrons. 2. For main group elements, the number of valence electrons equals eight minus the element's group number. 3. Core electrons are not involved in bonding or in chemical reactions.

1 and 3

82. Three possible structures of C2H2Cl2 are shown below. Which of these molecules are polar?

1 and 3

12. How many valence electrons are present in the Lewis formula for the chlorite ion, Cl^2-?

20

57. What is the molecular geometry around carbon atom C1?

trigonal planar

87. Use Lewis structures to predict the bond order for a sulfur-oxygen bond in the sulfite ion?

4/3

30. How many different molecules have the molecular formula C6H14?

5

49. When you draw the Lewis structure for PF2Cl3, how many single bonds, double bonds, and lone pair electrons reside on the central phosphorus atom?

5 single bonds, 0 double bonds, 0 lone pairs

45. How many lone pairs are present around the central atom in the Lewis structure of SF6?

0

89. Using bond-energy data, what is ΔrH for the following reaction? CH4(g) + 2Cl2(g) → CCl4(g) + 2H2(g) Bond Bond Energy (kJ/mol) C-H 413 H-H 432 Cl-Cl 242 C-Cl 328

-40 kJ/mol-rxn

34. What is the formal charge on the O2 atom in the following Lewis structure?

1

86. Use Lewis structures to predict the bond order for a sulfur-oxygen bond in SO32-?

1

9. In the Lewis formula for sulfur dioxide, SO2, the number of lone pairs of electrons around the sulfur atom is

1

5. Which of the following statements is/are CORRECT? 1. Ionic bonds form when one or more valence electrons are transferred from one atom to another. 2. Covalent bonds involve sharing of electrons between atoms. 3. In most covalently bonded compounds, electrons are NOT shared equally between the atoms.

1, 2, and 3

68. What are the approximate H−N−H bond angles in NH4+?

109.5°

70. Which of the following is the approximate O−S−O bond angle in the sulfite ion, SO32-?

109.5°

22. How many hydrogen atoms are needed to complete the following hydrocarbon structure?

12

55. What is the bond angle in a trigonal planar molecule or ion?

120°

88. Based on the following data, what is the F-F bond energy? H2(g) + F2(g) → HF(g); ΔrH = -272.5 kJ/mol-rxn Bond Bond Energy (kJ/mol) H-H 435 H-F 565

150 kJ/mol

69. What is the O−C−N bond angle in OCN-?

180°

35. What is the formal charge of the oxygen atom in the Lewis structure for cyanate shown below?

2

26. Which of the following are possible Lewis structures for a molecule with the formula C2H6O?

2 and 3

85. Determine the bond order of NO+?

3

38. Which of the following are the correct resonance structures for the formate ion, HCO2-?

3 and 4

31. Which of the following statements concerning the formal charge of an atom is/are true? 1. The formal charge of each individual atom in a molecule or ion is the actual atomic charge that can be determined experimentally. 2. The formal charge of each individual atom is always the same for each possible resonance form. 3. The sum of the formal charges of each atom in an ion equals the overall charge of the molecule or ion.

3 only

92. Use the bond energies provided to complete the following statement. ________ when all of the bonds in acetic acid (CH3COOH) are broken. Bond Bond Energy (kJ/mol) C-H 413 C-O 358 O-H 463 C=O 745 C-C 348 C=C 614

3153 kJ/mol of energy is consumed

11. What is the total number of electrons (both lone and bond pairs) in the Lewis structure of SO4^2-?

32

71. What are the approximate F−Br−F bond angles in BrF5?

90° and 180°

40. Which of the following molecules or ions does not have one or more resonance structures?

H2CO

77. Choose which central atom in the following molecules is most electronegative.

H2O

52. Which of the following molecules or ions are likely to be free radicals: N2O, NO, and NO2?

NO and NO2

46. Which of the following has an incomplete octet in its Lewis structure?

NO2

79. Atoms having equal or nearly equal electronegativities are expected to form

nonpolar covalent bonds

28. The nitrogen atom in the cyanide ion, CN-, is surrounded by:

one triple bond and one lone pair of electrons.

54. What is the electron-pair geometry around an atom in a molecule or ion which is surrounded by two lone pairs of electrons and three single bonds.

trigonal bipyramidal

99. The rings in the nitrogen-containing bases in DNA are all flat with _____ electron-pair geometry around each atom.

trigonal-planar

62. Use VSEPR theory to predict the molecular geometry of BrO3-.

trigonal-pyramidal

29. The central atom in N2O is a nitrogen atom. This nitrogen atom is surrounded by

two double bonds and no lone pairs of electrons.

27. The molecule H2S has

2 bonding pairs and 2 lone pairs

33. What is the formal charge on each atom in dichloromethane, CH2Cl2?

C atom = 0, each H atom = 0, and each Cl atom = 0

74. Which of the following compounds has polar covalent bonds: CCl4, Cl2, HCl, and KCl?

CCl4 and HCl

1. Which of the following groups of molecules contains no ionic compounds?

CH2O, H2S, and NH3

16. Which of the following molecules or ions will have a Lewis structure most like that of phosphorus trichloride, PCl3?

ClO^3-

78. Rank the following covalent bonds in order of decreasing polarity: C-H, N-H, O-H, and F-H.

F-H > O-H > N-H > C-H

8. The given representation of an atom is called the _____.

Lewis dot structure

2. Which combination of atoms is most likely to produce a compound with ionic bonds?

Mg and O

36. One resonance structure for OCN- ion is drawn below. What is the formal charge on each atom?

O atom = -1, C atom = 0, and N atom = 0

13. Which of the following molecules or ions are isoelectronic: SO3, NF3, NO^3-, CO3^2-?

O3, NO^3- and CO3^2-

4. Which of the following pairs of compounds contains ionic bonds?

RbBr and MgS

3. Which combination of atoms is most likely to produce a compound with covalent bonds?

S and Cl

41. The Lewis structure of which of the following molecules violates the octet rule?

SF4

67. Based on electron-pair geometries, which of the following molecules has the smallest bond angle between any two adjacent atoms?

SF6

39. Which of the following exhibits resonance?

SO2

81. Which of the following molecules is polar?

SO2

76. Three nonequivalent Lewis structures for carbonyl sulfide, SCO, are given below. Use the concepts of formal charge and electronegativity to choose the structure that is the best representation.

Structure B, because all the formal charges equal 0

58. Use VSEPR theory to predict the electron-pair geometry and the molecular geometry of nitrogen trichloride, NCl3.

The electron-pair geometry is tetrahedral, the molecular geometry is trigonal-pyramidal.

60. According to VSEPR theory, which of the following is the correct statement concerning the electron-pair geometry and the molecular geometry of sulfur dioxide?

The electron-pair geometry is trigonal-planar, and the molecular geometry is bent.

59. Use VSEPR theory to predict the electron-pair geometry and the molecular geometry of boron tribromide, BBr3.

The electron-pair geometry is trigonal-planar, the molecular geometry is trigonal-planar.

64. According to VSEPR theory, which of the following is the correct molecular geometry around the carbon atom in formaldehyde?

Trigonal-planar

83. Linus Pauling noticed that the energy of a polar bond is often greater than expected. He attributed the greater bond energy to

a coulombic attraction between atoms with partially positive and negative charges.

66. Use VSEPR theory to predict the molecular geometry around the nitrogen atom in nitrite ion, NO2-.

bent

84. In molecules, as bond order increases,

bond length decreases and bond energy increases.

65. Use VSEPR theory to predict the molecular geometry of BrF5.

square-pyramidal

53. What is the molecular geometry around an atom in a molecule or ion which is surrounded by zero lone pairs of electrons and four single bonds.

tetrahedral

98. The backbone of DNA consists of the atoms O—P—O—C—C—C. Each atom has a(n) _____ electron-

tetrahedral

75. Electronegativity is a measure of _____.

the ability of an atom in a molecule to attract electrons to itself