Chapter 8 Basic Concepts of Chemical Bonding

Chemistry, The Central Science, 10th edition

Theodore L. Brown; H. Eugene LeMay, Jr.;and Bruce E. Bursten

Chapter 8Basic Concepts of Chemical Bonding

Troy WoodUniversity of BuffaloBuffalo, NY 2006, Prentice Hall

The electron configuration: 1s22s22p53s23p64s23d

7 is consistent with which atom?

1. Fe2. Co3. Cu4. Ni

Correct Answer:

The electron configuration [Ar]4s23d

7 corresponds to cobalt.

1. Fe2. Co3. Cu4. Ni

The electron configuration of Fe3+ is which of the following?

1. 1s22s22p53s23p64s23d6

2. 1s22s22p53s23p64s23d3

3. 1s22s22p53s23p63d5

4. 1s22s22p53s23p64s13d4

Correct Answer:

1. 1s22s22p53s23p64s23d6

2. 1s22s22p53s23p64s23d3

3. 1s22s22p53s23p63d5

4. 1s22s22p53s23p64s13d4

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

1. NaCl < LiCl < MgCl2

2. LiCl < NaCl < MgCl2

3. MgCl2 < NaCl < LiCl

Correct Answer:

1. NaCl < LiCl < MgCl2

2. LiCl < NaCl < MgCl2

3. MgCl2 < NaCl < LiCl

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.

Which of the following carbon–carbon atom bonds would be expected to be the shortest?

1. CC

2. CC

3. CC

1. CC

2. CC

3. CC

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.

Based on the electronegativities of the atoms, which of the following bonds would you predict is most polar?

1. CC2. CN3. CO4. CSi5. CBr

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.

1. CC2. CN3. CO4. CSi5. CBr

Boron (B) has an electronegativity of 2.0; chlorine (Cl) has an electronegativity of 3.0. Which of the following BEST describes a BCl bond? 1. Ionic

2. Polar covalent

3. Nonpolar covalent

1. Ionic

2. Polar covalent

3. Nonpolar covalent

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.

Which of the following molecules has a zero dipole moment?

1. HF

2. H2O

3. CS2

4. CHCl3

Correct Answer:

1. HF

2. H2O

3. CS2

4. CHCl3

Even though each C=S bond is polar, their dipole vector quantities cancel each other out, and CS2 has no net dipole.

Which of the following BEST describes the formal charges on the atoms in the cyanide ion, CN ?

1. C = +1, N = 1

2. C = 1, N = +1

3. C = 0, N = 1

4. C = 1, N = 0

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 = 1N: 5 valence e 5 e = 0

1. C = +1, N = 1

2. C = 1, N = +1

3. C = 0, N = 1

4. C = 1, N = 0

Which is predicted to have the longest carbon–oxygen bonds: CO, CO2, or CO3

2?

1. CO32

2. CO2

3. CO

Correct Answer:

In CO, the carbon–oxygen bond is a triple bond, while in CO2 both carbon–oxygen bonds are double bonds. In CO3

2, there are three resonance structures and the average carbon–oxygen bond is 1 1/3.

1. CO32

2. CO2

3. CO

1. 467 kJ2. +467 kJ3. +17 kJ4. 983 kJ

Calculate H from the following bond enthalpies for the reaction:

2 NCl3 N2 + 3 Cl2D(NCl) = 200, D(NN) = 941, D(ClCl) = 242 (all kJ/mol).

Correct Answer:

H = (bond enthalpies of bonds broken) ( bond enthalpies of bonds formed)

H = 6(200) [941 + 3(242)]

H = 1200 (1667)

H = 467

1. 467 kJ2. +467 kJ3. +17 kJ4. 983 kJ