CHAPTER 4:

THE COVALENT BOND

Valence Electrons

4-1. Which of the following elements has five valence electrons?

(a) Ca (b) Ga (c) Ge (d) As (e) Se

Answer: (d)

4-2. How many valence electrons are in the IF₂^- ion?

          (a) 7 (b) 14 (c) 20 (d) 21 (e) 22

Answer: (e)

Electronegativity and Bond Polarity

4-3. Which of the following elements is the most electronegative?

           (a) S (b) As (c) P (d) Se (e) Cl

Answer: (e)

4-4. Which of the following lists the elements in the correct order of increasing electronegativity?

(a) Si < S < 0 (b) S < Si < 0 (c) S < O < Si (d) Si < O < S (e) O < Si < S

Answer: (a)

4-5. Which series of elements is arranged in order of decreasing electronegativity?

(a) C, Si, P, As, Se (b) O, P, Al, Mg, K (c) Na, Li, B, N, F

          (d) K, Mg, Be, O, N (e) Li, Be, B, C, N

Answer: (b)

4-6. Given the following electronegativities: K = 0.8, H = 2.2, and I = 2.5 which of the following statements is true?

           (a) H₂, I₂ and HI are nonpolar covalent compounds.

          (b) KI is nonpolar covalent and HI is ionic.

          (c) HI is nonpolar covalent and I₂ is polar covalent.

          (d) H₂ is nonpolar covalent, while HI and KI are ionic.

          (e) none of the above are true.

Answer: (a)

4-7. In which of the following compounds is the bond the most ionic?

          (a) BeF₂ (b) CaCl₂ (c) SrBr₂ (d) BaF₂ (e) CaI₂

Answer: (d)

4-8. In which of the following compounds is the bond the least polar?

           (a) NaCl (b) CH₄ (c) CO (d) Cl₂ (e) HCl

Answer: (d)

4-9. Which of the following would form compounds with fluorine in which the bond is the least ionic?

(a) P (b) Ca (c) Al (d) O (e) Se

Answer: (d)

4-10. Which of the following compounds is most likely to be on the borderline between ionic and covalent compounds?

          (a) MgO (b) MgBr₂ (c) Al₂O₃ (d) AlF₃ (e) AlBr₃

Answer: (e)

Lewis Structure

4-11. Which of the following atoms, ions or molecules could combine to form a stable covalent bond?

          (a) CH₄ and H^- (b) BF₃ and F^- (c) H and F^- (d) Ar and BF₃ (e) Ar and CH₄

Answer: (b)

4-12. The correct Lewis structure for CH₂Cl₂ contains:

          (a) 2 single bonds, 2 double bonds and no nonbonding electrons

          (b) 4 single bonds and no nonbonding electrons

          (c) 4 single bonds and four nonbonding electrons

          (d) 2 single bonds, 2 double bonds, and eight nonbonding electrons

           (e) 4 single bonds and 12 nonbonding electrons.

Answer: (e)

4-13. The correct Lewis structure for the NO₂⁺ ion has:

           (a) 2 double bonds and eight nonbonding electrons

          (b) 1 double bond, 1 single bond, and 12 nonbonding electrons

          (c) 2 single bonds and 12 nonbonding electrons

          (d) 2 triple bonds and 4 nonbonding electrons

          (e) 1 single bond, 1 double bond, and 8 nonbonding electrons

Answer: (a)

4-14. Which of the following are exceptions to the Lewis octet rule?

(I) CO₂ (II) BeF₂ (III) SF₄ (IV) SO₃ (V) PCl₃

          (a) I and II (b) II and III (c) III and IV

          (d) I, II and III (e) none of these are exceptions to the Lewis octet rule

Answer: (b)

4-15. Which of the following are exceptions to the Lewis octet rule?

(I) BF₃ (II) H₂CO (III) XeF₄ (IV) H₃O⁺ (V) ClF₃

          (a) I and II (b) I and III (c) I, III and V

          (d) II and III (e) III and V

Answer: (c)

4-16. Which of the following compounds contains only single bonds?

(a) CN^- (b) NO⁺ (c) CO (d) O₂^2- (e) Cl₂CO

Answer: (d)

4-17. Which of the following would be the best Lewis structure for NOCl?

Answer: (c)

4-18. Which of the following compounds would have the same electron configuration as the N₂ molecule?

                      (I) CaO (II) CO (III) NO (IV) CN^- (V) NO⁺

          (a) I (b) II and IV (c) II and III  (d) II, IV and V (e) IV and V

Answer: (d)

4-19. Which of the following would have a Lewis structure most like that of CO₃^2- ion?

(a) CH₃⁺ (b) NH₃ (c) NO₃^- (d) SO₃^2- (e) SO₄^2-

Answer: (c)

4-20. Which of following molecules is best described with two resonance structures?

(a) NO₂^- (b) H₂O (c) OF₂ (d) ClNO (e) BeF₂

Answer: (a)

4-21. Which of the following isn’t a resonance hybrid?

           (a) CO₂ (b) NO₂^- (c) N₂O (d) SO₃ (e) SCN^-

Answer: (a)

4-22. Which of the following are resonance hybrids?

                     (I) HCO₂^- (II) PH₃ (III) HCN (IV) SO₄^2- (V) NO₂

          (a) I (b) II and IV (c) IV and V

          (d) I and IV (e) I and V

Answer: (e)

4-23. Which of the following compounds contains the strongest carbon-nitrogen bond? (Hint: Look at their Lewis structures)

          (a) H₂CNH (b) HCN (c) H₃CNH₂ (d) H₃CNO

          (e) all of these molecules contain C-N single bonds.

Answer: (b)

4-24. Which of the following elements would form a compound with the following Lewis structure?

(a) Be (b) B (c) C (d) N (e) O (f) F

Answer: (d)

4-25. If there are two pairs of nonbonding electrons in the valence shell of the central atom in the XF₄^- ion, in which Group of the periodic table does the element X belong?

          (a) Group IVA (b) Group VA (c) Group VIA

           (d) Group VIIA (e) Group VIIIA

Answer: (d)

4-26. What is element X in the following Lewis structure?

(a) B (b) C (c) N (d) O (e) F

Answer: (c)

4-27. Which element will combine with sulfur to form a linear molecule with the formula XS₂? (a) Li (b) Be (c) C (d) O (e) F

Answer: (c)

4-28. Which element would form an XF₆^2- ion for which there are no nonbonding electrons in the Lewis structure?

          (a) N (b) Al (c) Si (d) P (e) Br

Answer: (c)

4-29. If X is a 3rd row element and XO₂ has the Lewis structure

X must be:

          (a) Al (b) Si (c) P (d) S (e) Cl

Answer: (d)

4-30. If the XF₆^- ion has the Lewis structure

          X could be which of the following elements?

          (a) N (b) Al (c) Si (d) P (e) Br

Answer: (d)

4-31. Assume that the XF₃ molecules has the following Lewis structure.

The molecule could be:

(a) boron trifluoride, i.e., X = B

(b) nitrogen trifluoride, i.e., X = N

(c) chlorine trifluoride, i.e., X = Cl

(d) phosphorus trifluoride, i.e., X = P

(e) more than one of the above

Answer: (a)

4-32. Nitrous oxide (N₂O) is an anesthetic commonly known as “laughing gas.” In spite of the brilliant performance by Steve Martin in the movie “The Little Shop of Horrors,” it doesn’t always induce laughing. Sometimes people get hysterical. Which of the following is a correct Lewis structure for this compound?

Answer: (c)

Formal Charge

4-33. In lecture, we analyzed the formal charge on the so-called “zwitterion” form of the amino acid glycine: H₃N⁺CH₂CO₂^-. The properties of the various amino acids depend heavily on the presence (or absence) of charge on the side chain. Consider the amino acid arginine, for example, which has the following Lewis structure:

Once again, there is a positive charge on the amine on the amino acid backbone, which we can ignore. What about the nitrogens labeled 1, 2 and 3 on the side chain? Are they neutral, negatively charged, or positively charged?

(a) N(1) = 0, N(2) = +1, and N(3) = 0

                     (b) N(1) = 0, N(2) = -1, and N(3) = 0

                     (c) N(1) = +1, N(2) = 0, and N(3) = +1

                     (d) N(1) = -1, N(2) = 0, and N(3) = -1

                     (e) N(1) = +1, N(2) = 0, and N(3) = -1

4-34. The American response to the attack on World Trade Center involved using 40-year old B-52's to drop cluster bombs on Afghanistan. Our response to the anthrax scare was a 20-year old antibacterial known as ciprofloxacin or “Cipro.”

Apply the concept of formal charge to the three nitrogen atoms labeled 1, 2 and 3 on the side chain? Are they neutral, negatively charged, or positively charged?

(a) N(1) = -1, N(2) = -1, and N(3) = -1

                     (b) N(1) = -1, N(2) = 0, and N(3) = 0

                     (c) N(1) = 0, N(2) = 0, and N(3) = 0

                     (d) N(1) = 0, N(2) = +1, and N(3) = +1

                     (e) N(1) = +1, N(2) = +1, and N(3) = +1

Bonding and Nonbonding Pairs

4-35. How many pairs of bonding electrons are in the valence shell of the iodine atom in the IF₂^- ion?

          (a) 0 (b) 1 (c) 2 (d) 3 (e) 4

Answer: (c)

4-36. How many pairs of nonbonding electrons are in the valence shell of the iodine atom in the IF₂^- ion?

          (a) 0 (b) 1 (c) 2 (d) 3 (e) 4

Answer: (d)

4-37. How many pairs of nonbonding electrons are in the valence shell of the iodine atom in the ICl₄^- ion?

          (a) 0 (b) 1 (c) 2 (d) 3 (e) 4

Answer: (c)

4-38. How many nonbonding electrons are on the central atom in the Lewis structure of xenon tetrafluoride?

          (a) 0 (b) 1 (c) 2 (d) 3 (e) 4

Answer: (e)

4-39. How many pairs of bonding electrons can be found in the valence shell of the nitrogen atom in HNO₂? (Hint: the skeleton structure is HONO)

          (a) 0 (b) 1 (c) 2 (d) 3 (e) 4

Answer: (d)

4-40. How many pairs of nonbonding electrons can be found on the chlorine atom in chlorous acid, HOClO?

          (a) 0 (b) 1 (c) 2 (d) 3 (e) 4

Answer: (c)

4-41. Which of the following elements would form an XF₆^2- ion that has no nonbonding electrons in the valence shell of the central atom?

          (a) Ca (b) C (c) Si (d) S (e) P

Answer: (c)

4-42. Which of the following species has all its electrons paired?

          (a) Fe³⁺ (b) Zn²⁺ (c) ClO₂ (d) NO (e) NO₂

Answer: (b)

Molecular Geometry

4-43. In which compound are the valence electrons on the sulfur arranged towards the corners of a tetrahedron?

           (a) SF₃⁺ (b) SF₄ (c) SF₅ (d) SF₆ (e) both SF₄ and SF₆

Answer: (a)

4-44. What is the distribution of electrons around the S atom in H₂SO₄? [Hint: The skeleton structure of this oxyacid is O₂S(OH)₂.]

          (a) linear (b) trigonal planar (c) tetrahedral

          (d) trigonal bipyramidal (e) octahedral

Answer: (c)

4-45. What is the distribution of electrons around the N atom in HNO₃? (Hint: The skeleton structure of this oxyacid is HONO₂)

          (a) linear (b) trigonal planar (c) tetrahedral

          (d) trigonal bipyramidal (e) octahedral

Answer: (b)

4-46. There is a single pair of nonbonding electrons on the central atom in the Lewis structure of ICl₅. This molecule has:

(a) A trigonal pyramidal distribution of electrons and an octahedral molecular geometry

           (b) An octahedral distribution of electrons and a square pyramidal geometry

(c) A trigonal bipyramidal distribution of electrons and a see-saw molecular geometry

          (d) An octahedral distribution of electrons and a trigonal bipyramidal geometry

          (e) A trigonal bipyramidal distribution of electrons and trigonal bipyramidal geometry.

Answer: (b)

4-47. The bond angles in most symmetric, AB_x, molecules are the same. Which of the following is an exception to this rule?

          (a) NH₃ (b) SF₆ (c) PCl₅ (d) SO₃ (e) CO₂

Answer: (c)

4-48. Which term best describes the shape of the I₃^- ion?

           (a) linear (b) bent (c) trigonal planar

          (d) trigonal pyramidal (e) trigonal bipyramidal

Answer: (a)

4-49. What is the molecular geometry of the compound formed by the reaction of nitrogen with fluorine?

          (a) bent (b) trigonal planar (c) trigonal pyramidal

          (d) trigonal bipyramidal (e) none of the above

Answer: (c)

4-50. What is the molecular geometry of the SF₅⁺ ion?

          (a) see-saw (b) square planar (c) square pyramidal

           (d) trigonal bipyramidal (e) octahedral

Answer: (d)

4-51. What is the molecular geometry of xenon tetrafluoride?

          (a) tetrahedral (b) trigonal bipyramidal (c) see-saw

           (d) square planar (e) octahedral

Answer: (d)

4-52. The shape of the NO₂^- ion is best described as:

          (a) linear (b) T-shaped (c) bent

          (d) square planar (e) pyramidal

Answer: (c)

4-53. What is the best description of the structure of the SF₃⁺ ion?

          (a) bent or angular (b) trigonal planar (c) trigonal pyramidal

          (d) tetrahedral (e) trigonal bipyramidal

Answer: (c)

4-54. The molecular structure of the IO₃^- ion is best described as:

          (a) bent or angular (b) trigonal planar (c) trigonal pyramidal

          (d) trigonal bipyramidal (e) T-shaped

Answer: (c)

4-55. Which of the following molecules is a Lewis acid that has a trigonal planar shape?

          (a) BeCl₂ (b) PCl₃ (c) Ca(OH)₂ (d) BF₃ (e) H₃O⁺

Answer: (d)

4-56. Which of the following molecules are best described as bent or angular in shape?

                      (I) H₂S (II) CO₂ (III) ClNO (IV) NH₂^- (V) O₃

          (a) I and II (b) I, III and IV (c) I, III, IV and V

          (d) II, III and IV (e) All of these molecules are bent or angular in shape

Answer: (c)

4-57. Which of the following molecules are planar?

                     (I) SO₃ (II) SO₃^2- (III) NO₃^- (IV) PF₃ (V) BH₃

          (a) I and II (b) I and III (c) I, III and V  (d) II and IV (e) III and V

Answer: (c)

4-58. Which of the following molecules are tetrahedral?

                     (I) SiF₄ (II) CH₄ (III) NF₄⁺ (IV) BF₄^- (V) TeF₄

          (a) I and II (b) I, II and III (c) I, II, III and IV

          (d) II, III and IV (e) V

Answer: (c)

4-59. Which of the following molecules are linear?

                     (I) C₂H₂ (II) CO₂ (III) NO₂^- (IV) NO₂⁺ (V) H₂O

          (a) I and II (b) I, II and III (c) I, II and IV

          (d) II and III (e) V

Answer: (c)

4-60. Which of the following has a square-planar shape?

          (a) SF₄ (b) ClO₄^- (c) CCl₄ (d) ICl₄^- (e) PO₄^3-

Answer: (d)

4-61. Which of the following compounds have the same shape or geometry?

           (a) NH₂^- and H₂O (b) NH₂^- and BeH₂

          (c) H₂O and BeH₂ (d) NH₂^-, H₂O and BeH₂

Answer: (a)

4-62. Which of the following compounds have the same shape or geometry?

          (a) SF₄ and CH₄ (b) CO₂ and H₂O (c) CO₂ and BeH₂

          (d) N₂O and NO₂ (e) PCl₄⁺ and PCl₄^-

Answer: (c)

4-63. Which of the following molecules or ions doesn’t have a tetrahedral shape?

          (a) SiF₄ (b) NF₄⁺ (c) BF₄^- (d) SeF₄ (e) CF₄

Answer: (d)

4-64. Which of the following molecules or ions isn’t planar?

(a) NH₃ (b) BF₃ (c) CO₃^2- (d) NO₃^-

          (e) all of these molecules or ions are planar.

Answer: (a)

4-65. Which of the following species isn’t planar?

          (a) SO₃ (b) SO₃^2- (c) SO₂ (d) BF₃ (e) NO₃^-

Answer: (b)

4-66. According to the VSED theory, the distribution of electrons in the valence shell of the central atom of a molecule can be predicted from the Lewis structure of that molecule. What is the distribution of electrons in the valence shell of the Xe atom in the XeF₃⁺ ion?   (a) trigonal planar (b) tetrahedral (c) square planar

           (d) trigonal bipyramidal (e) octahedral

Answer: (d)

4-67. What would be the best description of the shape of the XeF₃⁺ ion?

          (a) linear (b) bent (c) see-saw (d) T-shape (e) tetrahedral

Answer: (d)

4-68. Tellurium hydride is one of the foulest smelling compounds known. How many pairs of nonbonding electrons are in the valence shell of the tellurium atom in TeH₂?

          (a) 0 (b) 1 (c) 2 (d) 3 (e) 4

Answer: (c)

4-69. What is the best description of the distribution of electrons in the valence shell of the tellurium atom in TeH₂?

          (a) linear (b) trigonal planar (c) tetrahedral

          (d) trigonal bipyramidal (e) octahedral

Answer: (c)

4-70. What is the best description of the shape of the TeH₂ molecules?

          (a) linear (b) bent (c) trigonal planar (d) tetrahedral (e) see-saw

Answer: (b)

4-71. The best way for the body to get rid of excess nitrogen from the metabolism of proteins is by excreting urea, a planar molecule which has the following Lewis structure.

Which element does the "X" stand for in this Lewis structure?

(a) C (b) N (c) O (d) P (e) S

Answer: (a)

4-72. If there is a single pair of nonbonding electrons on the "X" atom in the Lewis structure of XF₄, in which group of the periodic table would you be the most likely to find element "X"?

          (a) Group IlIA (b) Group IVA (c) Group VA (d) Group VIA (e) Group VIIA

Answer: (d)

4-73. What would be the distribution of electrons in the valence shell of the "X" atom in the previous question?

           (a) trigonal planar (b) tetrahedral (c) trigonal bipyramidal

           (d) octahedral (e) none of these

Answer: (c)

4-74. What would be the shape of the XF₄ molecule in the previous questions?

          (a) octahedral (b) see-saw (c) tetrahedral

          (d) square pyramidal (e) trigonal bipyramidal

Answer: (b)

4-75. Which element would form a neutral XF₃ molecule with a trigonal planar geometry?

          (a) Be (b) B (c) C (d) N (e) Cl

Answer: (b)

4-76. The compound XCl₃ has a trigonal pyramidal geometry. Element Z is a member of:

(a) Group IIA (b) Group IlIA (c) Group VA (d) Group VIA (e) Group VIIA

Answer: (c)

4-77. Last year, Stan Freeburg noted three names that occupied so much of the news in recent years – Monica Lewinsky (the White House aid), Tara Lipinski (The Olympic Champion), and Theodore Kaczynski (the Unabomber) – all rhyme. Obviously a conspiracy! During the peak years of the witch-hunt for communist conspiracies, Marie Curie’s daughter – Irene Curie Joliot – was turned down for membership in the American Chemical Society solely because she was a communist. This led Linus Pauling, one of the foremost chemists of the 20^th century, to resign from the ACS. Pauling won two Nobel Prizes, one for chemistry and one for peace. One of his many contributions was the theory of hybridization, with which he explained the observed shapes of molecules. Which of the following set of hybrid orbitals would give rise to an trigonal bipyramidal geometry?

                     (a) sp (b) sp² (c) sp³ (d) sp³d (e) sp³d²

Answer: (d)

4-78. An element we will represent as X forms a compound with the empirical formula XCl₅ that undergoes an interesting reaction when it crystallizes to form a mixed salt of XCl₄⁺ and XCl₆^- ions. Assume that XCl₄⁺ has a tetrahedral geometry and there are no nonbonding electrons in the valence shell of the X atom. In which column of the periodic table are you most likely to find element X?

          (a) Group IVA (C, Se, Ge ...)        (b) Group VA (N, P, As ...)

          (c) Group VIA (O, S, Se ...            (d) Group VIIA (F, Cl, Br ...)

          (e) Group VIIIA (He, Ne, Ar, ...)

Answer: (b)

4-79. Metformin is the chemical name for a prescription drug sold as “glucophage,” which is an oral hypoglycemic. In other words, a pill that lowers blood sugar levels, so that adult on-set diabetics don’t have to inject themselves with insulin. The Lewis structure of metformin is shown below.

Use the VSEPR or VSED theories to predict the geometry around the nitrogen atom in the center of the molecule, e.g., N(3).

          (a) bent or angular (b) trigonal planar (c) trigonal pyramidal

          (d) trigonal bipyramidal (e) tetrahedral

Answer: (c)

4-80. Terpin hydrate is an expectorant that was used for many years by people with serious coughs, such as those suffering from pneumonia.

Use the VSEPR theory to predict the distribution of electrons in the valence shell of the oxygen atoms in this compound.

(a) linear (b) bent or angular (c) trigonal planar (d) tetrahedral

          (e) trigonal bipyramidal

Answer: (d)

4-81. When the rare gas elements (He, Ne, Ar, Kr, Xe and Rn) were first discovered, a sample of Ar was sent to Moissan, who had discovered the most active of the known elements: F₂. The failure of Moissan's attempts to react argon with fluorine, coupled with repeated failures by other chemists to get the more abundant of these gases to undergo chemical reaction, eventually led to their being labeled inert gases. We now know this isn’t so. Xe reacts with F₂ to form a variety of compounds, including XeF₄. Which of the following best describes the XeF₄ molecule?

(a) Trigonal bipyramidal distribution of valence electrons on the Xe with a T-shaped molecular geometry.

(b) Trigonal bipyramidal distribution of valence electrons on the Xe with a trigonal planar molecular geometry.

(c) Trigonal bipyramidal distribution of valence electrons on the Xe with a pyramidal molecular geometry.

(d) Octahedral distribution of valence electrons on the Xe with a square planar molecular geometry.

(e) Octahedral distribution of valence electrons on the Xe with a see-saw molecular geometry.

Answer: (d)

4-82. At a seminar on “everything you want to know about research at Unilever” a chemist talked about how they used the blue complex that forms when the I₃^- ion is added to starch to stain dishes to test their new — and improved! — liquid detergent. How many pairs of nonbonding electrons are in the valence shell of the central iodine atom in the I₃^- ion?

                     (a) 0 (b) 1 (c) 2 (d) 3 (e) 4

Answer: (d)

4-83. The Raschig process involves the reaction between ammonia and the hypochlorite ion to form hydrazine, which has been used as a rocket fuel.

2 NH₃(aq) + OCl^-(aq) ➝ H₂NNH₂(g)

There are isolated cases of individuals making hydrazine unexpectedly in their homes when cleaning a commode. They start with a cleaner that contains ammonia, and then, when this doesn’t work, they mix it with a cleaner (such as Chlorox) that contains the hypochlorite ion. How many pairs of nonbonding electrons can be found on each nitrogen atom in the hydrazine molecule? (Note: Assume that there is a bond between the two nitrogen atoms in hydrazine.)

          (a) 0 (b) 1 (c) 2 (d) 3

          (e) The two N atoms contain a different number of nonbonding electrons.

Answer: (b)

4-84. Predict the distribution of electrons in the valence shell of the nitrogen atoms in hydrazine.

          (a) linear (b) bent or angular (c) trigonal planar

          (d) trigonal pyramidal (e) tetrahedral

Answer: (e)

4-85. Use the VSEPR theory to predict the geometry around each nitrogen atom in hydrazine.

(a) linear (b) bent or angular (c) trigonal planar

                     (d) trigonal pyramidal (e) tetrahedral

Answer: (d)

Hybridization

4-86. Which type of hybrid orbitals are used by the carbon atom in CO₂?

(a) sp (b) sp² (c) sp³ (d) dsp³ (e) d²sp³

Answer: (a)

4-87. In which of the following compounds is the central nitrogen atom sp² hybridized?

(a) NO₂⁺ (b) NO₂ (c) NO₂^- (d) NO₃^- (e) NO₂, NO₂^- and NO₃^-

Answer: (e)

4-88. What is the hybridization of the nitrogen atom in the N₂ molecule?

(a) sp (b) sp² (c) sp³ (d) sp³d (e) sp³d²

Answer: (a)

4-89. What is the hybridization of central iodine atom in the I₃^- ion?

(a) sp (b) sp² (c) sp³ (d) sp³d (e) sp³d²

Answer: (d)

4-90. What is the hybridization of the sulfur atom in the SF₃⁺ ion?

(a) sp (b) sp² (c) sp³ (d) sp³d (e) sp³d²

Answer: (c)

4-91. What is the hybridization of the beryllium atom in BeF₂?

(a) sp (b) sp² (c) sp³ (d) sp³d (e) sp³d²

Answer: (a)

4-92. What is the hybridization of the xenon atom in the XeF₃⁺ ion?

(a) sp (b) sp² (c) sp³ (d) sp³d (e) sp³d²

Answer: (d)

4-93. What is the hybridization of the nitrogen atom in the NO₂⁺ ion?

(a) sp (b) sp² (c) sp³ (d) sp³d (e) sp³d²

Answer: (a)

4-94. The central atom in all of the following compounds has the same hybridization, except: (a) NO₂^- (b) CO₃^2- (c) BF₃ (d) NH₃

(e) the hybridization is the same in all of these compounds

Answer: (d)

Molecular Orbital Theory

4-95. As noted in last year’s exam, the drug for which more prescriptions – and more bad jokes – were written recently has the scientific name Sildenafil citrate and the trade name Viagra™. Viagra™ works by inducing the release of nitrogen oxide (NO) from endothelial cells, which diffuses into the smooth muscles where it binds to an enzyme called guanylate cyclase, which induces the synthesis of cyclic GMP, which induces the muscle cells to release Ca²⁺ ions, which allows the muscle cells to relax, which allows blood to flow, and so on. Use the following molecular orbital diagram to predict which of the following has the largest bond order:

          (a) NO⁺ (b) NO (c) NO^- (d) all of the above have the same bond order

Answer: (a)

4-96. Use the same molecular orbital diagram to predict which of the following molecules should be paramagnetic.

                     (I) B₂ (II) C₂ (III) N₂ (IV) O₂ (V) F₂

          (a) I (b) I and II (c) I and IV (d) I, II and IV (e) II, III and IV

Answer: (c)