Chapter 5
The Covalent Bond
5-1
1. What two opposing forces dictate the bond length? (Why do bonds form and what keeps the bonds from getting
any shorter?)
The bond length is the distance at which the repulsion of the two nuclei equals the attraction of the valence
electrons on one atom and the nucleus of the other.
3. List the following bonds in order of increasing bond length: H-Cl, H-Br, H-O.
H-O < H-Cl < H-Br. The order of increasing atom size.
5. Use electronegativities to describe the nature (purely covalent, mostly covalent, polar covalent, or ionic) of the
following bonds.
a) P-Cl Δχ = 3.0 – 2.1 = 0.9 polar covalent b) K-O Δχ = 3.5 – 0.8 = 2.7 ionic
c) N-H Δχ = 3.0 – 2.1 = 0.9 polar covalent d) Tl-Br Δχ = 2.8 – 1.7 = 1.1 polar covalent
7. Name the following compounds:
a) S2Cl2 disulfur dichloride b) CCl4 carbon tetrachloride
c) PCl5 phosphorus pentachloride d) HCl hydrogen chloride
9. Write formulas for each of the following compounds:
a) dinitrogen tetroxide N2O4 b) nitrogen monoxide NO c) dinitrogen pentoxide N2O5
11. Consider the U-V, W-X, and Y-Z bonds. The valence orbital diagrams for the orbitals involved in the bonds are
shown in the margin. Use an arrow to show the direction of the bond dipole in the polar bonds or indicate “not
polar” for the nonpolar bond(s). Rank the bonds in order of increasing polarity.
The bond dipole points toward the more electronegative atom in the bond, which is the atom with the lower
energy orbital. The magnitude of the dipole increases as the electronegativity difference (orbital energy
difference) increases. The W-X bond is not polar because the orbital energies of W and X are identical, and
the Y-Z bond in more polar than the U-V bond because the energy separation of the bonding orbitals is
greater. W-X < U-V < Y-Z
13. Use an arrow to indicate the bond dipole direction in each of the following bonds:
a) S-O b) C-H c) O-H d) C-O
→ ←∗ ← → Note the C-H bond is essentially nonpolar.
15. Use only the position of the atoms on the periodic table to list the following bonds in order of decreasing polarity:
a) S-O, Se-O, As-O As-O > Se-O > S-O Increasing electronegativity of non-oxygen atom
b) F-F, H-F, N-F H-F > N-F > F-F Increasing electronegativity of non-fluorine atom
c) P-Cl, Sb-Cl, Sn-Cl Sn-Cl > Sb-Cl > P-Cl Increasing electronegativity of non-chlorine atom
17. For each of the species listed below, indicate the number of electrons required to give each atom an octet or duet
(ER), the number of valence electrons (VE), and the number of shared pairs (SP) in the Lewis structure.
a) N2O4 b) CH4O c) HBrO2 d) S2O82-
ER 6(8) = 48 2(8) + 4(2) = 24 3(8) + 2 = 26 10(8) = 80
VE 2(5) + 4(6) = 34 4 + 4(1) + 6 = 14 1 + 7 + 2(6) = 20 10(6) + 2 = 62
SP 1/2 (48 - 34) = 7 1/2 (24 - 14) = 5 1/2 (26 - 20) = 3 1/2 (80 - 62) = 9
