Chapter 16B?Bonding and Molecular
Structure: Fundamental Concepts
MULTIPLE CHOICE
1. For an atom of a main group element, the number of valence electrons is equal to
| a. | its number of core electrons. |
| b. | the principle quantum number of its outer shell. |
| c. | its period number. |
| d. | its group number. |
| e. | eight minus its group number. |
ANS: D OBJ: 9.1 Valence Electrons
3. A silicon atom has ____ valence electrons.
| a. | 0 |
| b. | 2 |
| c. | 4 |
| d. | 6 |
| e. | 10 |
ANS: C OBJ: 9.1 Valence Electrons
4. Which combination of atoms is most likely to produce a compound with ionic bonds?
| a. | Al and F |
| b. | P and H |
| c. | C and O |
| d. | Si and O |
| e. | S and Br |
10. What is the total number of valence electrons in a carbon dioxide molecule?
| a. | 4 |
| b. | 8 |
| c. | 16 |
| d. | 20 |
| e. | 22 |
ANS: C OBJ: 9.4 Covalent Bonding and
Lewis Structures
12. Which of the following molecules or ions are isoelectronic: SO2, CO2, NO2-, ClO2-?
| a. | SO2 and CO2 |
| b. | SO2 and NO2- |
| c. | CO2 and ClO2- |
| d. | NO2- and ClO2- |
| e. | SO2, NO2-, and ClO2- |
ANS: B OBJ: 9.4 Covalent Bonding and
Lewis Structures
13. If two or more species have the same number of electrons resulting in similar Lewis structures, they are said to be ____.
| a. | neutral |
| b. | resonant structures |
| c. | symmetric |
| d. | isoelectronic |
| e. | covalent |
ANS: D OBJ: 9.4 Covalent Bonding and
Lewis Structures
14. How many lone-pair electrons are on the carbon atom in CO2?
| a. | 0 |
| b. | 1 |
| c. | 2 |
| d. | 3 |
| e. | 4 |
ANS: A OBJ: 9.4 Covalent Bonding and
Lewis Structures
15. Which of the following species will have a Lewis structure most like that of carbon disulfide, CS2?
| a. | NO2- |
| b. | SO2 |
| c. | H2S |
| d. | SF2 |
| e. | SCN- |
ANS: E OBJ: 9.4 Covalent Bonding and
Lewis Structures
16. Which of the following species will have a Lewis structure most like that of the hydronium ion, H3O+?
| a. | NO3- |
| b. | NH3 |
| c. | SO3 |
| d. | CO32- |
| e. | H2CO |
ANS: B OBJ: 9.4 Covalent Bonding and
Lewis Structures
17. How many lone-pair electrons surround each nitrogen atom in hydrazine, N2H4?
| a. | 0 |
| b. | 1/2 |
| c. | 1 |
| d. | 3 |
| e. | 4 |
ANS: C OBJ: 9.4 Covalent Bonding and
Lewis Structures
18. Which of the following is a correct
Lewis structure for ozone, O3?
| a. | 1 |
| b. | 2 |
| c. | 3 |
| d. | 4 |
| e. | 5 |
ANS: E OBJ: 9.4 Covalent Bonding and
Lewis Structures
19. Which of the following is a correct
Lewis structure for N2O?
| a. | 1 |
| b. | 2 |
| c. | 3 |
| d. | 4 |
| e. | 5 |
ANS: B OBJ: 9.4 Covalent Bonding and
Lewis Structures
20. Which of the following is a correct
Lewis structure for the phosphate ion?
| a. | 1 |
| b. | 2 |
| c. | 3 |
| d. | 4 |
| e. | 5 |
ANS: A OBJ: 9.4 Covalent Bonding and
Lewis Structures
21. Which of the following are possible
Lewis structures for C2H6O?
| a. | 1 |
| b. | 2 |
| c. | 3 |
| d. | 2 and 3 |
| e. | 1, 2, and 3 |
ANS: D OBJ: 9.4 Covalent Bonding and
Lewis Structures
22. Which of the following are resonance
structures for sulfur dioxide, SO2?
| a. | 1 and 2 |
| b. | 2 and 4 |
| c. | 3 and 4 |
| d. | 1, 2, and 3 |
| e. | 2, 3, and 4 |
ANS: B OBJ: 9.5 Resonance
23. Which of the following are resonance
structures for the formate ion, HCO2-?
| a. | 1 and 2 |
| b. | 2 and 3 |
| c. | 3 and 4 |
| d. | 1, 3, and 4 |
| e. | 2, 3, and 4 |
ANS: C OBJ: 9.5 Resonance
24. How many resonance structures can be drawn for the thiocyanate ion, SCN-? The carbon atom is in the center of this ion.
| a. | 1 |
| b. | 2 |
| c. | 3 |
| d. | 4 |
| e. | 5 |
ANS: C OBJ: 9.5 Resonance
25. Which of the following elements is most likely to form a molecular structure that disobeys the octet rule?
| a. | Ne |
| b. | C |
| c. | B |
| d. | F |
| e. | Cl |
ANS: E OBJ: 9.6 Exceptions to the Octet
Rule
26. Which of the following elements is most likely to form a molecular structure that disobeys the octet rule?
| a. | B |
| b. | C |
| c. | N |
| d. | O |
| e. | F |
ANS: A OBJ: 9.6 Exceptions to the Octet
Rule
27. When both of the electrons in a molecular bond originate from the same atom, the bond is called a(n)
| a. | double bond. |
| b. | coordinate covalent bond. |
| c. | pi bond. |
| d. | sigma bond. |
| e. | ionic bond. |
ANS: B OBJ: 9.6 Exceptions to the Octet
Rule
28. What is the correct Lewis structure
for ICl4-?
| a. | 1 |
| b. | 2 |
| c. | 3 |
| d. | 4 |
| e. | 5 |
ANS: D OBJ: 9.6 Exceptions to the Octet
Rule
29. What is the correct Lewis structure
for IF3?
| a. | 1 |
| b. | 2 |
| c. | 3 |
| d. | 4 |
| e. | 5 |
ANS: B OBJ: 9.6 Exceptions to the Octet
Rule
30. The central atom in XeF4 is surrounded by
| a. | 3 single bonds, 1 double bond, and no lone pairs of electrons. |
| b. | 2 single bonds, 2 double bonds, and no lone pairs of electrons. |
| c. | 3 single bonds, 1 double bond, and 1 lone pair of electrons. |
| d. | 4 single bonds, no double bonds, and no lone pairs of electrons. |
| e. | 4 single bonds, no double bonds, and 2 lone pairs of electrons. |
ANS: E OBJ: 9.6 Exceptions to the Octet
Rule
31. The central atom in IF2- is surrounded by
| a. | no single bonds, 2 double bonds, and no lone pairs of electrons. |
| b. | no single bonds, 2 double bonds, and 2 lone pairs of electrons. |
| c. | 1 single bond, 1 double bond, and 1 lone pair of electrons. |
| d. | 2 single bonds, no double bonds, and 2 lone pairs of electrons. |
| e. | 2 single bonds, no double bonds, and 3 lone pairs of electrons. |
ANS: E OBJ: 9.6 Exceptions to the Octet
Rule
32. Which of the following species will have a Lewis structure most like that of SF4?
| a. | XeF4 |
| b. | SO42- |
| c. | ICl4+ |
| d. | PF4+ |
| e. | IO4- |
ANS: C OBJ: 9.6 Exceptions to the Octet
Rule
33. Which of the following molecules or ions are likely to be free radicals: N2O, NO, OCl-, and ClO2?
| a. | N2O only |
| b. | N2O and NO |
| c. | NO and OCl- |
| d. | NO and ClO2 |
| e. | OCl- and ClO2 |
ANS: D OBJ: 9.6 Exceptions to the Octet
Rule
34. Use VSEPR theory to predict the electron-pair geometry and the molecular geometry of the nitrite ion, NO2-.
| a. | The electron-pair geometry is linear, the molecular geometry is linear. |
| b. | The electron-pair geometry is trigonal-planar, the molecular geometry is bent. |
| c. | The electron-pair geometry is trigonal-planar, the molecular geometry is linear. |
| d. | The electron-pair geometry is tetrahedral, the molecular geometry is bent. |
| e. | The electron-pair geometry is tetrahedral, the molecular geometry is linear. |
ANS: B OBJ: 9.7 Molecular Shapes
35. Use VSEPR theory to predict the electron-pair geometry and the molecular geometry of iodine trichloride, ICl3.
| a. | The e--pair geometry is trigonal-planar, the molecular geometry is trigonal-planar. |
| b. | The e--pair geometry is tetrahedral, the molecular geometry is trigonal-pyramidal. |
| c. | The e--pair geometry is tetrahedral, the molecular geometry is trigonal-planar. |
| d. | The e--pair geometry is trigonal-bipyramidal, the molecular geometry is T-shaped. |
| e. | The e--pair geometry is trigonal-bipyramidal, the molecular geometry is trigonal-planar. |
ANS: D OBJ: 9.7 Molecular Shapes
36. Use VSEPR theory to predict the molecular geometry of H3O+.
| a. | trigonal-pyramidal |
| b. | trigonal-planar |
| c. | bent |
| d. | T-shaped |
| e. | linear |
ANS: A OBJ: 9.7 Molecular Shapes
37. Use VSEPR theory to predict the molecular geometry of CS2.
| a. | linear |
| b. | bent |
| c. | trigonal-planar |
| d. | tetrahedral |
| e. | octahedral |
ANS: A OBJ: 9.7 Molecular Shapes
38. Use VSEPR theory to predict the molecular geometry of IF5.
| a. | tetrahedral |
| b. | see-saw |
| c. | trigonal-bipyramidal |
| d. | square-pyramidal |
| e. | octahedral |
ANS: D OBJ: 9.7 Molecular Shapes
39. Use VSEPR theory to predict the molecular geometry of CO32-.
| a. | bent |
| b. | tetrahedral |
| c. | trigonal-pyramidal |
| d. | T-shaped |
| e. | trigonal-planar |
ANS: E OBJ: 9.7 Molecular Shapes
40. What are the Cl-P-Cl bond angles in PCl3?
| a. | 109.5° |
| b. | 120° |
| c. | 109.5° and 120° |
| d. | 90° and 120° |
| e. | 90° and 180° |
ANS: A OBJ: 9.7 Molecular Shapes
41. What is the bond angle in N2O?
| a. | 90° |
| b. | 107° |
| c. | 109.5° |
| d. | 120° |
| e. | 180° |
ANS: E OBJ: 9.7 Molecular Shapes
42. What are the bond angles in ClO4-?
| a. | 90° |
| b. | 109.5° |
| c. | 120° |
| d. | 180° |
| e. | 90° and 180° |
ANS: B OBJ: 9.7 Molecular Shapes
43. Place the following molecules in order from smallest to largest bond angles: NH4+, NH3, and NH2-.
| a. | NH4+ < NH3 < NH2- |
| b. | NH4+ < NH2- < NH3 |
| c. | NH2- < NH3 < NH4+ |
| d. | NH2- < NH4+ < NH3 |
| e. | NH3 < NH2- < NH4+ |
ANS: C OBJ: 9.7 Molecular Shapes
44. What is the formal charge on each atom in a hypobromite ion, OBr-?
| a. | O = -2, Br = -1 |
| b. | O = -2, Br = +1 |
| c. | O = -1, Br = +1 |
| d. | O = -1, Br = 0 |
| e. | O = 0, Br = -1 |
ANS: D OBJ: 9.8 Charge Distribution
in Covalent Bonds and Molecules
45. One resonance structure for thiocyanate
ion is drawn below. What is the formal charge on each atom?
| a. | S = 0, C = -1, N = 0 |
| b. | S = 0, C = 0, N = -1 |
| c. | S = -1, C = 0, N = 0 |
| d. | S = 0, C = +2, N = -3 |
| e. | S = -2, C = +4, N = -3 |
ANS: B OBJ: 9.8 Charge Distribution
in Covalent Bonds and Molecules
46. Predict which of the following compounds will have the most polar covalent bond(s).
| a. | HF |
| b. | CBr4 |
| c. | H2S |
| d. | NCl3 |
| e. | HI |
ANS: A OBJ: 9.8 Charge Distribution
in Covalent Bonds and Molecules
47. Which one of the following molecules has a dipole moment?
| a. | CI4 |
| b. | PF5 |
| c. | NCl3 |
| d. | SO3 |
| e. | O2 |
ANS: C OBJ: 9.9 Molecular Polarity
48. Which one of the following molecules or ions has a dipole moment?
| a. | IO4- |
| b. | ICl2- |
| c. | SF4 |
| d. | XeF4 |
| e. | CO2 |
ANS: C OBJ: 9.9 Molecular Polarity
49. When bonding electrons are unequally shared, we say that the bond is polar. Linus Pauling noticed that the energy of a polar bond is often greater than expected. He attributed the greater bond energy to
| a. | a coulombic attraction between atoms with partially positive and negative charges. |
| b. | the greater bond lengths of the heteronuclear bonds. |
| c. | one of the many unexplainable phenomena that scientists encounter. |
| d. | the ability of heteronuclear species to form double and triple bonds. |
| e. | the higher number of valence electrons found in heteronuclear molecules. |
ANS: A OBJ: 9.10 Bond Properties: Order,
Length, and Energy
50. In molecules, as bond order increases,
| a. | both bond length and bond energy increase. |
| b. | both bond length and bond energy decrease. |
| c. | bond length increases and bond energy is unchanged. |
| d. | bond length is unchanged and bond energy increases. |
| e. | bond length decreases and bond energy increases. |
ANS: E OBJ: 9.10 Bond Properties: Order,
Length, and Energy
51. Use Lewis structures to predict the bond order for a nitrogen-oxygen bond in the nitrite ion, NO2-.
| a. | 1/2 |
| b. | 1 |
| c. | 4/3 |
| d. | 3/2 |
| e. | 3 |
ANS: D OBJ: 9.10 Bond Properties: Order,
Length, and Energy
52. The standard molar enthalpy of
formation of ClF3 is -405 kJ.
1/2 Cl2(g) + 3/2 F2(g) ? ClF3(g)
The bond energies of Cl2 and F2 are 242 kJ and 155 kJ/mol, respectively. Calculate the energy of an Cl-F bond.
| a. | 8 kJ/mol |
| b. | 87 kJ/mol |
| c. | 207 kJ/mol |
| d. | 253 kJ/mol |
| e. | 802 kJ/mol |
ANS: D OBJ: 9.10 Bond Properties: Order,
Length, and Energy
53. When heated, azomethane decomposes
into nitrogen gas and ethane gas.
CH3N=NCH3(g) ? N2(g)
+ C2H6(g)
Using average bond energies, calculate the enthalpy of reaction.
| a. | -611 kJ |
| b. | -527 kJ |
| c. | -429 kJ |
| d. | -313 kJ |
| e. | -263 kJ |
ANS: E OBJ: 9.10 Bond Properties: Order,
Length, and Energy
SHORT ANSWER
1. The molecular geometry of a molecule
whose central atom has three single bonds and two lone pairs of electrons
is ________.
ANS:
T-shaped
2. If a molecule has a positive and
a negative end, the molecule is said to have a ________ moment.
ANS:
dipole
3. In PCl5, the Cl-P-Cl
bond angle between an axial and an equatorial chlorine is ____ degrees.
ANS:
90
4. The ________ energy is the energy
of formation of one mole of a solid crystalline ionic compound from
gas phase ions.
ANS:
lattice
5. Three equivalent Lewis structures
can be drawn for carbonate ion. Each structure consists of two carbon-oxygen
single bonds and one carbon-oxygen double bond. These three equivalent
structures are referred to as ________ structures.
ANS:
resonance
6. One might expect H2O
to have a linear molecular geometry since its central atom is surrounded
by only two outer atoms. However, water has a bent geometry. Explain.
ANS:
The shape of a molecule is dependent
upon the number of electron-pairs surrounding the central atom. The
oxygen atom in water has four electron-pairs which are distributed around
the oxygen atom in a tetrahedral geometry. Thus, the bond angles are
approximately 109°,
not 180°.
7. The second ionization energy of
sodium is much greater than that of magnesium. Explain.
ANS:
Valence shell electrons are more easily removed than inner shell electrons because they are partially shielded from the nuclear charge by inner shell electrons. Only one electron occupies sodium's valence shell. The second ionization of sodium requires removal of an electron from an inner shell. For magnesium, both the first and second ionizations remove electrons from the valence shell.