Rucete ✏ AP Chemistry In a Nutshell
4. Covalent Compounds, Formulas, and Structures — Practice Questions 2
This chapter introduces the structure and geometry of covalent molecules, including Lewis structures, resonance, hybridization, and molecular polarity.
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(Multiple Choice — Click to Reveal Answer)
1. Which of the following molecules contains only sigma bonds?
(A) CH4
(B) C2H2
(C) CO2
(D) O2
Answer
(A) — CH4 has four single (sigma) bonds and no pi bonds.
2. What is the molecular geometry of BF4–?
(A) Trigonal planar
(B) Tetrahedral
(C) Seesaw
(D) Square planar
Answer
(B) — BF4– has four bonding pairs and no lone pairs, giving it a tetrahedral shape.
3. What is the main factor that determines the angle between bonds in a molecule?
(A) Atomic mass
(B) Valence bond energy
(C) Number of unpaired electrons
(D) Electron domain repulsion
Answer
(D) — According to VSEPR theory, electron domains repel and determine bond angles.
4. Which of the following has the shortest bond length?
(A) N–N
(B) N=N
(C) N≡N
(D) N–H
Answer
(C) — A triple bond (N≡N) results in the shortest bond length.
5. Which molecule has a central atom with a lone pair and three bonded atoms?
(A) CH4
(B) NH3
(C) BeCl2
(D) CO2
Answer
(B) — NH3 has three bonding pairs and one lone pair, forming a trigonal pyramidal shape.
6. What is the geometry of ICl3 according to VSEPR theory?
(A) Trigonal planar
(B) T-shaped
(C) Linear
(D) See-saw
Answer
(B) — ICl3 has two lone pairs and three bonds, giving it a T-shaped molecular geometry.
7. What hybrid orbitals are used in a molecule with a trigonal bipyramidal shape?
(A) sp3
(B) sp2
(C) sp3d
(D) sp3d2
Answer
(C) — A trigonal bipyramidal shape requires sp3d hybridization.
8. Which of the following is most likely to have an expanded octet?
(A) CCl4
(B) PCl5
(C) NH3
(D) CH2O
Answer
(B) — PCl5 has five bonding pairs around phosphorus, exceeding the octet.
9. Which element is capable of forming a molecule with a square planar geometry?
(A) B
(B) C
(C) Xe
(D) Be
Answer
(C) — Xenon can form compounds like XeF4 with square planar geometry due to its empty d orbitals.
10. What is the molecular geometry of a molecule with the AX2E3 configuration?
(A) Linear
(B) T-shaped
(C) Bent
(D) See-saw
Answer
(A) — AX2E3 has two bonding pairs and three lone pairs, leading to a linear geometry.
11. Which bond is most polar based on electronegativity differences?
(A) C–H
(B) N–O
(C) H–F
(D) C–Cl
Answer
(C) — The electronegativity difference between H and F is the greatest, making H–F the most polar bond.
12. In which molecule do all atoms lie in a single plane?
(A) NH3
(B) H2O
(C) SO3
(D) CH4
Answer
(C) — SO3 is trigonal planar and all atoms lie in the same plane.
13. Which molecule is nonpolar despite having polar bonds?
(A) CH3Cl
(B) H2O
(C) CO2
(D) NH3
Answer
(C) — CO2 has polar bonds, but its linear shape makes it nonpolar.
14. Which of the following molecules exhibits resonance?
(A) CH4
(B) CO3²⁻
(C) HCl
(D) CH3Cl
Answer
(B) — The carbonate ion has three resonance structures with delocalized electrons.
15. Which of the following is the best explanation for a bent molecular geometry?
(A) All bonding pairs
(B) One lone pair
(C) Two lone pairs
(D) No repulsion
Answer
(C) — Two lone pairs on the central atom (as in H2O) result in a bent geometry.
16. Which molecule has the greatest number of lone pairs on the central atom?
(A) CH4
(B) SF6
(C) H2O
(D) XeF2
Answer
(D) — XeF2 has three lone pairs on the central xenon atom.
17. The hybridization of the central atom in BeCl2 is:
(A) sp3
(B) sp2
(C) sp
(D) None
Answer
(C) — BeCl2 has two bonding domains, requiring sp hybridization.
18. Which of the following molecules is pyramidal in shape?
(A) CH4
(B) H2O
(C) NH3
(D) CO2
Answer
(C) — NH3 has three bonds and one lone pair, resulting in a trigonal pyramidal shape.
19. Which of the following best describes the bonding in ozone (O3)?
(A) One single and one double bond
(B) Alternating single and double bonds
(C) Two equivalent bonds due to resonance
(D) One triple bond and a lone pair
Answer
(C) — Ozone has two resonance structures that average into two equivalent bonds.
20. Which type of molecule would have an ideal bond angle of 120°?
(A) Linear
(B) Tetrahedral
(C) Trigonal planar
(D) Octahedral
Answer
(C) — Trigonal planar molecules have 120° bond angles.
21. What is the hybridization of the carbon atom in formaldehyde (CH2O)?
(A) sp
(B) sp2
(C) sp3
(D) sp3d
Answer
(B) — CH2O has three electron domains around carbon, leading to sp2 hybridization.
22. Which molecule has an angular or bent shape?
(A) BeCl2
(B) CO2
(C) H2O
(D) BF3
Answer
(C) — Water has two bonding pairs and two lone pairs, giving it a bent shape.
23. Which of the following would have a bond angle closest to 90°?
(A) CH4
(B) SF6
(C) BF3
(D) NH3
Answer
(B) — SF6 has octahedral geometry with 90° bond angles.
24. How many pi bonds are in ethene (C2H4)?
(A) 0
(B) 1
(C) 2
(D) 3
Answer
(B) — Ethene contains one double bond, which includes one pi bond.
25. Which of the following species has sp3d2 hybridization?
(A) PCl3
(B) SF6
(C) XeF2
(D) SO2
Answer
(B) — SF6 has six bonding pairs, requiring sp3d2 hybrid orbitals.
26. Which of the following molecules has exactly two pi bonds and three sigma bonds?
(A) C2H4
(B) C2H2
(C) CO2
(D) HCN
Answer
(C) — CO2 has two double bonds (each with one pi and one sigma), totaling 2 pi and 2 sigma bonds, plus one sigma in the central carbon, for three sigma total.
27. Which combination of hybridization and geometry is incorrect?
(A) sp — linear
(B) sp2 — trigonal planar
(C) sp3d — octahedral
(D) sp3 — tetrahedral
Answer
(C) — sp3d leads to trigonal bipyramidal geometry; octahedral corresponds to sp3d2.
28. Which molecule has a central atom with more than one lone pair and exhibits a linear shape?
(A) BeCl2
(B) XeF2
(C) CO2
(D) N2O
Answer
(B) — XeF2 has three lone pairs and two bonding pairs on Xe, forming a linear shape.
29. The geometry of IF5 is:
(A) Trigonal bipyramidal
(B) Square pyramidal
(C) Octahedral
(D) Tetrahedral
Answer
(B) — IF5 has five bonding pairs and one lone pair on iodine, giving a square pyramidal shape.
30. Which compound has delocalized electrons in a conjugated π system?
(A) CH3CH3
(B) CH2CHCH2
(C) C6H6
(D) H2O
Answer
(C) — Benzene (C6H6) has a conjugated π system with delocalized electrons over the ring.
31. Which of the following has the greatest bond angle distortion due to lone pairs?
(A) CH4
(B) NH3
(C) H2O
(D) PF5
Answer
(C) — H2O has two lone pairs, which cause more repulsion and distortion than NH3’s one lone pair.
32. In which molecule is the central atom sp2 hybridized and the molecule bent in shape?
(A) CO2
(B) SO2
(C) CH4
(D) NO3⁻
Answer
(B) — SO2 has two bonding regions and one lone pair on sulfur, making it sp2 and bent.
33. Which of the following has the lowest bond order?
(A) O2⁻
(B) O2
(C) O2⁺
(D) NO
Answer
(A) — O2⁻ has a bond order of 1.5, which is lower than that of the others.
34. Which statement is true about dative (coordinate covalent) bonds?
(A) They occur only in ionic compounds
(B) Both bonding electrons come from the same atom
(C) They are weaker than hydrogen bonds
(D) They only occur between halogens
Answer
(B) — In a dative bond, both electrons come from a single donor atom (e.g., NH4⁺).
35. Which of the following species cannot be described without violating the octet rule?
(A) NO2
(B) NH4⁺
(C) BeF2
(D) SF6
Answer
(D) — SF6 has 12 valence electrons around sulfur, which exceeds the octet.
36. What is the molecular geometry and hybridization of the central atom in ClF3?
Answer
T-shaped, sp3d — ClF3 has five electron domains (3 bonding, 2 lone pairs) around the central atom, resulting in a T-shaped geometry and sp3d hybridization.
37. Explain why NH4⁺ is a stable molecule even though it contains a dative bond.
Answer
Because once formed, all bonds are indistinguishable — The lone pair on nitrogen forms a dative bond with a proton, creating a stable tetrahedral NH4⁺ ion where all N–H bonds are equivalent.
38. Describe how formal charge is used to identify the most stable resonance structure.
Answer
Lowest formal charges preferred — Structures with formal charges closest to zero and negative charges on more electronegative atoms are typically most stable.
39. Why does SF6 not follow the octet rule, and how is this justified?
Answer
Expanded octet due to d orbitals — Sulfur is in Period 3 and can use empty d orbitals to accommodate more than 8 electrons, allowing six fluorine bonds.
40. Identify the type of hybridization used by the central atom in XeF4 and describe the molecular geometry.
Answer
sp3d2, square planar — XeF4 has six electron domains (4 bonding, 2 lone pairs), resulting in sp3d2 hybridization and a square planar molecular geometry.
41. What is the bond angle in a molecule with AX5 (trigonal bipyramidal) geometry and where do lone pairs preferentially reside?
Answer
90°, 120°, 180°; equatorial positions — Lone pairs prefer equatorial positions in trigonal bipyramidal structures to minimize repulsion.
42. How does molecular polarity differ from bond polarity?
Answer
Molecular polarity is the vector sum — Bond polarity arises from differences in electronegativity, while molecular polarity depends on both bond polarity and molecular geometry.
43. Why does NO have an odd number of electrons, and what is its geometry?
Answer
11 valence electrons; linear geometry — NO is a free radical with an odd number of electrons, and its geometry is linear due to two atoms.
44. Determine the number of sigma and pi bonds in the molecule HC≡CH (ethyne).
Answer
3 sigma, 2 pi — There are two sigma bonds (C–H and C–C) and two pi bonds in the triple bond between carbons.
45. Describe the geometry and bonding in the nitrate ion (NO3⁻).
Answer
Trigonal planar with resonance — NO3⁻ has three equivalent N–O bonds due to resonance, forming a planar triangular shape.
46. What factors determine the strength of a covalent bond?
Answer
Bond order, bond length, atomic size — Higher bond order and shorter bond length typically lead to stronger bonds; smaller atoms form stronger bonds.
47. Explain why the central atom in PF5 can exceed the octet rule.
Answer
Access to d orbitals — Phosphorus is in Period 3 and can use its empty 3d orbitals to expand its valence shell beyond 8 electrons.
48. What is the difference between electron geometry and molecular geometry?
Answer
Electron geometry includes lone pairs — Electron geometry considers all electron domains; molecular geometry only includes bonding pairs, affecting the shape seen in the molecule.
49. What geometry results from an atom with two bonding pairs and one lone pair?
Answer
Bent (angular) — Three total domains (2 bonds + 1 lone pair) yield a bent shape with a bond angle slightly less than 120°.
50. Why is the bond angle in CH4 larger than in H2O?
Answer
Fewer lone pairs in CH4 — CH4 has no lone pairs, so electron repulsion is lower and the angle remains at 109.5°, while H2O has two lone pairs that compress the bond angle to ~104.5°.