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Problem 71a,c
State whether each of these statements is true or false. (a) The longer the bond, the stronger the bond. (c) A typical double bond length is in the 500–1000 pm range.
Problem 71e
State whether each of these statements is true or false. (e) The longer the bond, the more energy is stored chemical bonds.
- State whether each of these statements is true or false. (a) An oxygen–oxygen double bond is shorter than an oxygen–oxygen single bond. (b) The C—C bond in ethene is longer than the C—C bond in polyethene.
Problem 72
- We can define average bond enthalpies and bond lengths for ionic bonds, just like we have for covalent bonds. Which ionic bond is predicted to be stronger, Na—Cl or Ca—O?
Problem 73
- We can define average bond enthalpies and bond lengths for ionic bonds, just like we have for covalent bonds. Which ionic bond is predicted to have the smaller bond enthalpy, Li—F or Cs—F?
Problem 74
- Predict the length of the carbon–carbon bond you would expect if two H2C molecules reacted with each other by a combination reaction.
Problem 75
- Draw the Lewis structure for NO+ . Is the nitrogen– oxygen bond in NO+ longer, shorter, or the same length as the nitrogen–oxygen bond in NO? Explain. Draw the Lewis structure for NO+ .
Problem 76
- A new compound has a C—O bond length of 120 pm. Is this bond likely to be a single, double, or triple C—O bond?
Problem 77
Problem 79a
Consider the lattice energies of the following Group 2A compounds: BeH2, 3205 kJ/mol; MgH2, 2791 kJ/mol; CaH2, 2410 kJ/mol; SrH2, 2250 kJ/mol; BaH2, 2121 kJ/mol. (a) What is the oxidation number of H in these compounds?
Problem 79c
Consider the lattice energies of the following Group 2A compounds: BeH2, 3205 kJ/mol; MgH2, 2791 kJ/mol; CaH2, 2410 kJ/mol; SrH2, 2250 kJ/mol; BaH2, 2121 kJ/mol. (c) Consider BeH2. Does it require 3205 kJ of energy to break one mole of the solid into its ions, or does breaking up one mole of solid into its ions release 3205 kJ of energy?
Problem 79d
Consider the lattice energies of the following Group 2A compounds: BeH2, 3205 kJ/mol; MgH2, 2791 kJ/mol; CaH2, 2410 kJ/mol; SrH2, 2250 kJ/mol; BaH2, 2121 kJ/mol. (d) The lattice energy of ZnH2 is 2870 kJ/mol. Considering the trend in lattice enthalpies in the Group 2 compounds, predict which Group 2 element is most similar in ionic radius to the Zn2+ ion.
- A metal oxide has a lattice energy in the range of 3300 kJ/mol. Is the charge on the metal ion M likely to be 1+, 2+, or 3+? Explain.
Problem 81
Problem 82a
The ionic compound CaO crystallizes with the same structure as sodium chloride (Figure 8.3). (a) In this structure, how many O2- are in contact with each Ca2+ ion (Hint: Remember the pattern of ions shown in Figure 8.3 repeats over and over again in all three directions.)
- Construct a Born–Haber cycle for the formation of the hypothetical compound NaCl2, where the sodium ion has a 2+ charge (the second ionization energy for sodium is given in Table 7.2). (b) If we were to estimate the lattice energy of NaCl2 to be roughly equal to that of MgCl2 (2326 kJ/mol from Table 8.1), what value would you obtain for the standard enthalpy of formation, _x001F_Hf°, of NaCl2?
Problem 83
Problem 83a
Construct a Born–Haber cycle for the formation of the hypothetical compound NaCl2, where the sodium ion has a 2+ charge (the second ionization energy for sodium is given in Table 7.2). (a) How large would the lattice energy need to be for the formation of NaCl2 to be exothermic?
- A classmate of yours is convinced that he knows everything about electronegativity. (a) In the case of atoms X and Y having different electronegativities, he says, the diatomic molecule X–Y must be polar. Is your classmate correct? (b) Your classmate says that the farther the two atoms are apart in a bond, the larger the dipole moment will be. Is your classmate correct?
Problem 84
Problem 85a
Consider the collection of nonmetallic elements O, P, Te, I, and B. (a) Which two would form the most polar single bond?
Problem 85d
Consider the collection of nonmetallic elements: B, As, O, and I. (d) Which element would likely to participate in two covalent bonds?
Problem 86b
The substance chlorine monoxide, ClO(g), is important in atmospheric processes that lead to depletion of the ozone layer. The ClO molecule has an experimental dipole moment of 1.24 D, and the Cl — O bond length is 160 pm. (b) Based on the electronegativities of the elements, which atom would you expect to have a partial negative charge in the ClO molecule?
Problem 86c,d
The substance chlorine monoxide, ClO(g), is important in atmospheric processes that lead to depletion of the ozone layer. The ClO molecule has an experimental dipole moment of 1.24 D, and the Cl—O bond length is 160 pm. (c) Using formal charges as a guide, propose the dominant Lewis structure for the molecule. (g), is important in atmospheric processes that lead to depletion of the ozone layer. The ClO molecule has an experimental dipole moment of 1.24 D, and the Cl—O bond length is 160 pm. (d) The anion ClO exists. What is the formal charge on the Cl for the best Lewis structure for ClO-?
Problem 87b
(b) Using these partial charges and the atomic radii given in Figure 7.8, estimate the dipole moment of the molecule.
Problem 87c
(c) The measured dipole moment of BrCl is 0.57 D. If you assume the bond length in BrCl is the sum of the atomic radii, what are the partial charges on the atoms in BrCl using the experimental dipole moment?
Problem 88c
A major challenge in implementing the 'hydrogen economy' is finding a safe, lightweight, and compact way of storing hydrogen for use as a fuel. The hydrides of light metals are attractive for hydrogen storage because they can store a high weight percentage of hydrogen in a small volume. For example, NaAlH4 can release 5.6% of its mass as H2 upon decomposing to NaH(s), Al(s), and H2(g). NaAlH4 possesses both covalent bonds, which hold polyatomic anions together, and ionic bonds. (c) Based on electronegativity differences, predict the identity of the polyatomic anion. Draw a Lewis structure for this ion.
Problem 89b
Although I3- is a known ion, F3- is not. (b) One of your classmates says that F3- does not exist because F is too electronegative to make bonds with another atom. Give an example that proves your classmate is wrong.
Problem 90
Calculate the formal charge on the indicated atom in each of the following molecules or ions: (a) the central oxygen atom in O3 (b) phosphorus in PF6- (c) nitrogen in NO2 (d) iodine in ICl3 (e) chlorine in HClO4 (hydrogen is bonded to O).
Problem 91b
The hypochlorite ion, ClO-, is the active ingredient in bleach. The perchlorate ion, ClO4-, is a main component of rocket propellants. Draw Lewis structures for both ions. (b) What is the formal charge of Cl in the perchlorate ion, assuming the Cl—O bonds are all single bonds?
Problem 91c,d
The hypochlorite ion, ClO-, is the active ingredient in bleach. The perchlorate ion, ClO4-, is a main component of rocket propellants. Draw Lewis structures for both ions. (c) What is the oxidation number of Cl in the hypochlorite ion? (d) What is the oxidation number of Cl in the perchlorate ion, assuming the Cl—O bonds are all single bonds?
Problem 92a
The following three Lewis structures can be drawn for N2O:
(a) Using formal charges, which of these three resonance forms is likely to be the most important?
Problem 92b
The following three Lewis structures can be drawn for N2O:
(b) The N—N bond length in N2O is 1.12 Å, slightly longer than a typical N ≡N bond; and the N— O bond length is 1.19 Å, slightly shorter than a typical N ═O bond (see Table 8.4). Based on these data, which resonance structure best represents N2O?
Problem 94a
Ortho-Dichlorobenzene, C6H4Cl2, is obtained when two of the adjacent hydrogen atoms in benzene are replaced with Cl atoms. A skeleton of the molecule is shown here. (a) Complete a Lewis structure for the molecule using bonds and electron pairs as needed.