Chapter 2 — Quiz
Twenty questions. Answers at the end.
1. Carbon has how many valence electrons? (a) 2 (b) 4 (c) 6 (d) 8
2. A $2p$ orbital has: (a) Zero nodes. (b) One node (at the nucleus). (c) Two nodes. (d) Spherical symmetry.
3. The $C \equiv C$ triple bond consists of: (a) Three $\sigma$ bonds. (b) Three $\pi$ bonds. (c) One $\sigma$ + two $\pi$ bonds. (d) Two $\sigma$ + one $\pi$ bond.
4. In a Lewis structure of $CH_3Cl$, chlorine has: (a) 1 bond, 0 lone pairs. (b) 1 bond, 3 lone pairs. (c) 4 bonds, 0 lone pairs. (d) 2 bonds, 2 lone pairs.
5. The formal charge on oxygen in the hydronium ion, $H_3O^+$, is: (a) $-1$ (b) $0$ (c) $+1$ (d) $+2$
6. A carbon atom that is $sp^2$-hybridized has: (a) 4 $\sigma$-bonded neighbors + 0 lone pairs. (b) 3 $\sigma$-bonded neighbors + 0 lone pairs. (c) 2 $\sigma$-bonded neighbors + 1 lone pair. (d) 3 $\sigma$-bonded neighbors + 1 lone pair.
7. The geometry of a molecule with steric number 4 and no lone pairs is: (a) Linear. (b) Trigonal planar. (c) Tetrahedral. (d) Octahedral.
8. Water, $H_2O$, is bent (not linear) because: (a) Oxygen is $sp$-hybridized. (b) The two lone pairs on oxygen occupy space. (c) The two $O-H$ bond dipoles cancel. (d) Oxygen is more electronegative than hydrogen.
9. Resonance structures differ from each other only in: (a) The placement of atoms. (b) The placement of electrons. (c) The molecular formula. (d) Their bond angles.
10. The most-contributing resonance structure of a set is the one with: (a) The most formal charges. (b) The most electrons in $\pi$ bonds. (c) Complete octets and the fewest formal charges. (d) Negative charge on the most electropositive atom.
11. Which of the following has the largest bond dipole? (a) $C-H$ (b) $C-C$ (c) $C-O$ (d) $C-F$
12. In the formaldehyde molecule $H_2CO$, the carbon atom is: (a) $sp$-hybridized, linear geometry. (b) $sp^2$-hybridized, trigonal planar geometry. (c) $sp^3$-hybridized, tetrahedral geometry. (d) $sp^3$-hybridized, trigonal pyramidal geometry.
13. The HOMO of ethylene is: (a) A $\sigma$ bonding orbital. (b) A $\pi$ bonding orbital. (c) A $\sigma^*$ antibonding orbital. (d) A $\pi^*$ antibonding orbital.
14. In a molecular orbital diagram, combining two atomic orbitals produces: (a) One molecular orbital. (b) Two molecular orbitals. (c) Three molecular orbitals. (d) Four molecular orbitals.
15. The Pauling electronegativity of carbon is approximately: (a) 1.5 (b) 2.55 (c) 3.0 (d) 4.0
16. Which is the correct Lewis structure of $CO_2$? (a) $O - C - O$ (all single bonds) (b) $O = C = O$ (two double bonds) (c) $O \equiv C - O$ (one triple, one single) (d) $O - C \equiv O$ (one single, one triple)
17. A carbon atom bonded to four different groups is: (a) $sp^2$-hybridized. (b) Aromatic. (c) A stereocenter (chiral carbon). (d) Always acidic.
18. The bond length of a $C=C$ double bond is approximately: (a) 1.0 Å (b) 1.34 Å (c) 1.54 Å (d) 2.0 Å
19. Which molecule is expected to have a larger dipole moment? (a) $CO_2$ (linear). (b) $H_2O$ (bent). (c) $CH_4$ (tetrahedral). (d) $CCl_4$ (tetrahedral).
20. The concept of hybridization is used to: (a) Explain why carbon forms four bonds despite having only two unpaired electrons in the ground state. (b) Predict the color of a molecule. (c) Compute the exact wavefunction of a polyatomic molecule. (d) Determine the acidity of a compound.
Answers
- b. 2. b (node at the nucleus where the wavefunction changes sign). 3. c. 4. b. 5. c. 6. b. 7. c. 8. b. 9. b. 10. c. 11. d. 12. b. 13. b. 14. b. 15. b. 16. b. 17. c. 18. b. 19. b. 20. a.
Scoring: 17+ = ready for Chapter 3. 13–16 = re-read weak sections. Below 13 = re-read the chapter and do more exercises.