Rucete ✏ AP Chemistry In a Nutshell
4. Covalent Compounds, Formulas, and Structures — Practice Questions
This chapter introduces covalent bonding, Lewis structures, molecular geometry, hybridization, resonance, and molecular polarity.
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(Multiple Choice — Click to Reveal Answer)
1. Which of the following molecules has a tetrahedral shape?
(A) CH4
(B) CO2
(C) SO2
(D) H2O
Answer
(A) — Methane (CH4) has four bonding domains with no lone pairs, forming a tetrahedral geometry.
2. What does a double bond consist of?
(A) Two sigma bonds
(B) One sigma and one pi bond
(C) Two pi bonds
(D) One pi bond only
Answer
(B) — A double bond is composed of one sigma and one pi bond.
3. The geometry of ammonia (NH3) is:
(A) Tetrahedral
(B) Bent
(C) Trigonal planar
(D) Trigonal pyramidal
Answer
(D) — NH3 has three bonding pairs and one lone pair, giving it a trigonal pyramidal geometry.
4. Which of the following violates the octet rule?
(A) PCl5
(B) CH4
(C) NH3
(D) H2O
Answer
(A) — PCl5 contains 10 electrons around the phosphorus atom, exceeding the octet.
5. A molecule is nonpolar if:
(A) It contains only polar bonds
(B) It contains only nonpolar bonds
(C) It is symmetrical and the dipoles cancel out
(D) It has at least one lone pair on the central atom
Answer
(C) — Symmetrical molecules can be nonpolar if the dipole moments cancel.
6. Which of the following has sp2 hybridization?
(A) CH4
(B) BF3
(C) NH3
(D) C2H6
Answer
(B) — BF3 has three bonding domains and no lone pairs, indicating sp2 hybridization.
7. Which statement about SO2 is correct?
(A) It is linear and nonpolar
(B) It has resonance structures
(C) It contains no lone pairs on the central atom
(D) It has a trigonal bipyramidal shape
Answer
(B) — SO2 has resonance structures with one double bond delocalized across two oxygen atoms.
8. What type of molecule is CO2?
(A) Polar with trigonal planar shape
(B) Nonpolar with linear shape
(C) Polar with linear shape
(D) Nonpolar with bent shape
Answer
(B) — CO2 is linear and symmetrical, so it is nonpolar.
9. Which of the following has only sigma bonds?
(A) H2O
(B) CO2
(C) C2H2
(D) CH4
Answer
(D) — CH4 has only single (sigma) bonds.
10. What is the correct bond angle for a molecule with tetrahedral geometry?
(A) 180°
(B) 120°
(C) 109.5°
(D) 90°
Answer
(C) — A tetrahedral structure has bond angles of 109.5°.
11. Which of the following molecules has a bent molecular geometry?
(A) CH4
(B) H2O
(C) CO2
(D) CCl4
Answer
(B) — H2O has two bonding pairs and two lone pairs, giving it a bent shape.
12. What is the hybridization of the carbon atom in CO2?
(A) sp
(B) sp2
(C) sp3
(D) None
Answer
(A) — Carbon in CO2 forms two double bonds and has two electron domains, indicating sp hybridization.
13. Which of the following is a polar molecule?
(A) CO2
(B) CCl4
(C) CH3Cl
(D) BF3
Answer
(C) — CH3Cl is not symmetrical, making it polar.
14. Which of the following molecules contains a triple bond?
(A) CH4
(B) C2H4
(C) C2H2
(D) H2O
Answer
(C) — Acetylene (C2H2) contains a triple bond between the carbon atoms.
15. What does a lone pair on the central atom usually do to bond angles?
(A) Increases them
(B) Has no effect
(C) Decreases them
(D) Eliminates polarity
Answer
(C) — Lone pairs repel bonding pairs more strongly and reduce bond angles.
16. Which of the following molecules follows the octet rule?
(A) BF3
(B) PCl5
(C) CH4
(D) SF6
Answer
(C) — CH4 follows the octet rule with 8 electrons around carbon.
17. Which type of bond is the shortest?
(A) Single bond
(B) Double bond
(C) Triple bond
(D) Ionic bond
Answer
(C) — Triple bonds involve more shared electrons and are shorter.
18. What shape does SF6 exhibit?
(A) Trigonal bipyramidal
(B) Octahedral
(C) Tetrahedral
(D) Trigonal planar
Answer
(B) — SF6 has six bonding pairs, forming an octahedral shape.
19. Which bond has the greatest bond energy?
(A) C–C
(B) C=C
(C) C≡C
(D) C–H
Answer
(C) — Triple bonds have the highest bond energy.
20. In which molecule are all atoms in the same plane?
(A) H2O
(B) NH3
(C) SO3
(D) CH4
Answer
(C) — SO3 is trigonal planar, placing all atoms in one plane.
21. Which is the correct formal charge for oxygen in O3 (ozone) in one of its resonance forms?
(A) +1
(B) 0
(C) –1
(D) Depends on the structure
Answer
(D) — In resonance structures, formal charges can vary between atoms.
22. A nonpolar molecule with polar bonds is:
(A) CH3Cl
(B) H2O
(C) CO2
(D) NH3
Answer
(C) — CO2 has polar bonds, but due to linear symmetry, it's nonpolar.
23. The electron geometry around the oxygen atom in water is:
(A) Trigonal planar
(B) Linear
(C) Tetrahedral
(D) Trigonal pyramidal
Answer
(C) — Two lone pairs and two bonding pairs give oxygen a tetrahedral electron geometry.
24. Which molecule is an exception to the octet rule by having fewer than 8 electrons?
(A) CH4
(B) BeCl2
(C) NH3
(D) H2O
Answer
(B) — Beryllium in BeCl2 has only 4 valence electrons in its structure.
25. Which of the following shows delocalized electrons in resonance?
(A) CO
(B) SO3
(C) HCl
(D) CH4
Answer
(B) — In SO3, electrons are delocalized across resonance structures.
26. Which of the following molecules has an expanded octet?
(A) BF3
(B) PCl5
(C) CH4
(D) CO2
Answer
(B) — PCl5 has 10 electrons around phosphorus, exceeding the octet rule.
27. What hybridization is expected for the central atom in XeF4?
(A) sp3
(B) sp3d
(C) sp3d2
(D) sp2
Answer
(C) — XeF4 has six electron domains (4 bonding, 2 lone pairs), requiring sp3d2 hybridization.
28. Which of the following pairs is NOT correctly matched?
(A) sp3 — 109.5°
(B) Trigonal planar — 120°
(C) sp — 180°
(D) Square planar — 120°
Answer
(D) — Square planar molecules have 90° bond angles, not 120°.
29. Which compound has a central atom that does NOT follow the octet rule?
(A) NH3
(B) SF6
(C) CH2O
(D) CO2
Answer
(B) — SF6 has 12 valence electrons around sulfur, which is allowed due to its position in Period 3.
30. Which statement about resonance is correct?
(A) Resonance structures represent molecules rapidly flipping between forms
(B) Only one resonance structure exists in nature
(C) The true structure is a hybrid of all valid resonance forms
(D) Resonance applies only to aromatic compounds
Answer
(C) — Resonance indicates that the actual molecule is a hybrid of all valid structures.
31. In a molecule with AX2E2 geometry, what is the molecular shape and approximate bond angle?
(A) Linear, 180°
(B) Bent, 104.5°
(C) Trigonal planar, 120°
(D) Tetrahedral, 109.5°
Answer
(B) — AX2E2 geometry (like H2O) leads to a bent shape with bond angles around 104.5°.
32. Which of the following statements about bond order is FALSE?
(A) Bond order of 1 means a single bond
(B) Higher bond order means shorter bond length
(C) Bond order is always a whole number
(D) Resonance structures can result in fractional bond orders
Answer
(C) — Bond order can be fractional in cases involving resonance (e.g., 1.5 in benzene).
33. Which of the following compounds is planar and has delocalized electrons?
(A) CH4
(B) C2H6
(C) C6H6
(D) NH3
Answer
(C) — Benzene (C6H6) is planar with delocalized pi electrons in a conjugated system.
34. What causes the equal bond lengths in the nitrate ion (NO3–)?
(A) Hybrid orbitals
(B) Resonance
(C) Formal charge
(D) Electron affinity
Answer
(B) — Resonance delocalizes electrons across all three N–O bonds, making them equal in length.
35. Which of the following is LEAST relevant in determining bond strength?
(A) Bond order
(B) Bond polarity
(C) Bond length
(D) Vibrational frequency
Answer
(B) — While polarity affects properties, bond polarity itself doesn’t strongly determine bond strength.
36. Describe the molecular geometry and hybridization of the central atom in PCl3.
Answer
Trigonal pyramidal, sp3 — PCl3 has three bonding pairs and one lone pair, giving it sp3 hybridization and a trigonal pyramidal shape.
37. Explain why BF3 is nonpolar, even though the B–F bonds are polar.
Answer
Because of symmetry — The three polar bonds are arranged symmetrically in a trigonal planar geometry, so their dipole moments cancel out.
38. Why does the O–H bond in water lead to molecular polarity?
Answer
Due to bent shape and electronegativity difference — The bent structure and more electronegative oxygen result in a net dipole moment.
39. What is the formal charge on nitrogen in the nitrate ion (NO3–) using the most stable resonance form?
Answer
+1 — In the most stable resonance form, nitrogen has one double bond and two single bonds with a formal charge of +1.
40. Give the Lewis structure and molecular geometry of sulfur dioxide (SO2).
Answer
Bent shape with resonance — SO2 has one lone pair on sulfur and two resonance forms involving double bonds, giving a bent geometry.
41. Why is it impossible for nitrogen to form NCl5?
Answer
Because nitrogen cannot expand its octet — Nitrogen is in Period 2 and lacks d orbitals, so it can't hold more than 8 electrons.
42. Compare the bond angles in CH4, NH3, and H2O and explain the differences.
Answer
CH4 > NH3 > H2O — Lone pairs repel more strongly than bonding pairs, reducing bond angles in NH3 and H2O from the ideal tetrahedral angle.
43. What kind of hybridization occurs in carbon dioxide (CO2)?
Answer
sp hybridization — Carbon in CO2 has two double bonds and no lone pairs, leading to sp hybrid orbitals and a linear shape.
44. How many sigma and pi bonds are present in C2H2 (acetylene)?
Answer
3 sigma, 2 pi — There is one sigma bond between each atom and two pi bonds between the two carbon atoms.
45. Why is O2 paramagnetic according to molecular orbital theory?
Answer
Due to unpaired electrons — Molecular orbital diagrams show two unpaired electrons in the π* orbitals, making O2 paramagnetic.
46. Predict the molecular polarity of SF4 and explain your reasoning.
Answer
Polar — SF4 has a seesaw geometry with one lone pair, resulting in an asymmetrical shape and a net dipole moment.
47. Explain how resonance stabilizes the carbonate ion (CO3²–).
Answer
Delocalization of electrons — Resonance allows electrons to be spread evenly over all three oxygen atoms, lowering the potential energy and increasing stability.
48. What is the dipole moment, and what does it indicate about a molecule?
Answer
Dipole moment = charge × distance — It measures molecular polarity and indicates the separation of positive and negative charges in a molecule.
49. What determines whether a molecule with polar bonds is overall polar or nonpolar?
Answer
Shape and symmetry — If the molecular shape is symmetrical, polar bonds may cancel; if asymmetrical, the molecule is polar.
50. Why is the bond angle in H2O smaller than in NH3?
Answer
More lone pairs on oxygen — H2O has two lone pairs, which exert more repulsion than the one lone pair in NH3, reducing the bond angle further.