Chapter 8 Basic Concepts of Chemical Bonding

1. Chapter 8Basic Concepts of Chemical Bonding Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Troy Wood University of Buffalo Buffalo, NY  2006, Prentice Hall

2. The electron configuration: 1s22s22p53s23p64s23d7 is consistent with which atom? Fe Co Cu Ni

3. Correct Answer: The electron configuration [Ar]4s23d7 corresponds to cobalt. Fe Co Cu Ni

4. The electron configuration of Fe3+ is which of the following? 1s22s22p53s23p64s23d6 1s22s22p53s23p64s23d3 1s22s22p53s23p63d5 1s22s22p53s23p64s13d4

5. Correct Answer: 1s22s22p53s23p64s23d6 1s22s22p53s23p64s23d3 1s22s22p53s23p63d5 1s22s22p53s23p64s13d4

6. Arrange the following ionic compounds in order of increasing lattice energy: LiCl, NaCl, MgCl2 NaCl < LiCl < MgCl2 LiCl < NaCl < MgCl2 MgCl2 < NaCl < LiCl

7. Correct Answer: Lattice energy depends on size of the ions and their charges. MgCl2 has the highest lattice energy because it has a more positive cation. LiCl is higher than NaCl because the interatomic distance between cation and ion is shorter. NaCl < LiCl < MgCl2 LiCl < NaCl < MgCl2 MgCl2 < NaCl < LiCl

8. Which of the following carbon–carbon atom bonds would be expected to be the shortest? CC CC CC

9. Correct Answer: The bond length decreases as the bond enthalpy increases; in general, as the number of bonds between two atoms increases, the bond grows shorter and stronger. CC CC CC

10. Based on the electronegativities of the atoms, which of the following bonds would you predict is most polar? CC CN CO CSi CBr

11. Correct Answer: The difference in electronegativities is greatest between O (3.5) and C (2.5) for a net difference of 1.0. Each of the other combinations yields a smaller value for electronegativity difference. CC CN CO CSi CBr

12. Boron (B) has an electronegativity of 2.0; chlorine (Cl) has an electronegativity of 3.0. Which of the following BEST describes a BCl bond? Ionic Polar covalent Nonpolar covalent

13. Correct Answer: The difference in electronegativities is 1.0 because Cl = 3.0 and B = 2.0. This is too low to be an ionic bond but too high to be a nonpolar covalent bond. Ionic Polar covalent Nonpolar covalent

14. Which of the following molecules has a zero dipole moment? HF H2O CS2 CHCl3

15. Correct Answer: Even though each C=S bond is polar, their dipole vector quantities cancel each other out, and CS2 has no net dipole. HF H2O CS2 CHCl3

16. Which of the following BEST describes the formal charges on the atoms in the cyanide ion, CN ? C = +1, N = 1 C = 1, N = +1 C = 0, N = 1 C = 1, N = 0

17. Correct Answer: The formal charges are calculated from the difference between number of valence electrons and number of electrons assigned to each atom in the Lewis structure, thus: C: 4 valence e 5 e = 1 N: 5 valence e 5 e = 0 C = +1, N = 1 C = 1, N = +1 C = 0, N = 1 C = 1, N = 0

18. Which is predicted to have the longest carbon–oxygen bonds: CO, CO2, or CO32? CO32 CO2 CO

19. Correct Answer: In CO, the carbon–oxygen bond is a triple bond, while in CO2 both carbon–oxygen bonds are double bonds. In CO32, there are three resonance structures and the average carbon–oxygen bond is 1 1/3. CO32 CO2 CO

20. Calculate DH from the following bond enthalpies for the reaction: 2 NCl3 N2 + 3 Cl2 D(NCl) = 200, D(NN) = 941, D(ClCl) = 242 (all kJ/mol). 467 kJ +467 kJ +17 kJ 983 kJ

21. Correct Answer: DH =S(bond enthalpies of bonds broken)S ( bond enthalpies of bonds formed) DH =6(200)  [941 + 3(242)] DH = 1200  (1667) DH =  467 467 kJ +467 kJ +17 kJ 983 kJ