Chapter 11

The diagrams that follow illustrate two typical arrangements of paving bricks in a patio or driveway. Sketch the unit cell that corresponds to each pattern of bricks.

Make a sketch of a layer of sodium ions and chloride ions in a \(\mathrm{Na} \mathrm{Cl}\) crystal. Indicate how the ions are arranged in a face-centered cubic pattern, regardless of whether we place lattice points at the \(\mathrm{Cl}^{-}\) ions or the \(\mathrm{Na}^{+}\) ions.

Write the Bragg equation and define the symbols.

What kinds of particles are located at the lattice sites in a metallic crystal?

What kinds of attractive forces exist between particles in (a) molecular crystals, (b) ionic crystals, and (c) covalent crystals?

Why are covalent crystals sometimes called network solids?

What does the word amorphous mean?

What kinds of intermolecular attractive forces (i.e., dipole-dipole, London, and hydrogen bonding) are present in the following substances? (a) HF (b) \(\mathrm{PCl}_{3}\) (c) \(\mathrm{SF}_{6}\) (d) \(\mathrm{SO}_{2}\)

What kinds of intermolecular attractive forces are present in the following substances? (a) CC(=O)O (b) \(\mathrm{H}_{2} \mathrm{~S}\) (c) \(\mathrm{SO}_{3}\) (d) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\)

Consider the compounds \(\mathrm{CHCl}_{3}\) (chloroform, an important solvent that was once used as an anesthetic) and \(\mathrm{CHBr}_{3}\) (bromoform, which has been used as a sedative). Compare the strengths of their dipole-dipole attractions and the strengths of their London forces. Their boiling points are \(61^{\circ} \mathrm{C}\) and \(149^{\circ} \mathrm{C}\), respectively. For these compounds, which kinds of attractive forces (i.e., dipoledipole or London) are more important in determining their boiling points? Justify your answer.

Which of the following isomers of octane should have the higher viscosity? CCCCCCCC CC(C)(C)C(C)(C)C

Which should have the higher boiling point, ethanol \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH},\right.\) found in alcoholic beverages and fermented berries that are favored by wild bears) or ethanethiol \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{SH},\right.\) a foul-smelling liquid found in the urine of rabbits that have feasted on cabbage)?

How do the strengths of London forces compare in \(\mathrm{CO}_{2}(l)\) and \(\mathrm{CS}_{2}(l) ?\) Which of these is expected to have the higher boiling point? How would you check your answer?

What intermolecular forces must the following substances overcome in the process of vaporization? (a) ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\), (b) acetonitrile \(\left(\mathrm{H}_{3} \mathrm{CCN}\right)\), (c) phosphorus pentachloride \(\left(\mathrm{PCl}_{5}\right)\), and (d) sodium chloride \((\mathrm{NaCl})\)

What intermolecular attractions will be formed when the following substances condense from the gas phase? (a) hexane \(\left(\mathrm{C}_{6} \mathrm{H}_{14}\right)\), (b) acetone \(\left(\mathrm{H}_{3} \mathrm{CCOCH}_{3}\right)\), (c) iodine \(\left(\mathrm{I}_{2}\right),\) and (d) argon

The molar heat of vaporization of water at \(25^{\circ} \mathrm{C}\) is \(+43.9 \mathrm{~kJ} / \mathrm{mol}\). How many kilojoules of heat would be required to vaporize \(125 \mathrm{~mL}(0.125 \mathrm{~kg})\) of water?

The molar heat of vaporization of acetone, \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O},\) is \(30.3 \mathrm{~kJ} / \mathrm{mol}\) at its boiling point. How many kilojoules of heat would be liberated by the condensation of \(5.00 \mathrm{~g}\) of acetone?

Sketch the phase diagram for a substance that has a triple point at \(-57.0^{\circ} \mathrm{C}\) and \(5.10 \mathrm{~atm} .\) It has a vapor pressure of 1 atm at \(-78{ }^{\circ} \mathrm{C}\) and has a critical point at \(31^{\circ} \mathrm{C}\) and \(73 \mathrm{~atm} .\) Its solid expands as temperature increases.

We can determine the heat of vaporization by using the Clausius-Clapeyron equation if we know the vapor pressures of a substance at two different temperatures. Determine the heat of vaporization of diethyl ether if the vapor pressure is \(1.0 \mathrm{~mm} \mathrm{Hg}\) at \(-74.3^{\circ} \mathrm{C}\) and \(425 \mathrm{~mm} \mathrm{Hg}\) at \(18.7^{\circ} \mathrm{C}\)

The atomic radius of nickel is \(1.24 \AA\). Nickel crystallizes in a face- centered cubic lattice. What is the length of the edge of the unit cell expressed in angstroms and in picometers?

Silver forms face-centered cubic crystals. The atomic radius of a silver atom is \(144 \mathrm{pm}\). Draw the face of a unit cell with the nuclei of the silver atoms at the lattice points. The atoms are in contact along the diagonal. Calculate the length of an edge of this unit cell.

Potassium ions have a radius of \(133 \mathrm{pm},\) and bromide ions have a radius of \(195 \mathrm{pm}\). The crystal structure of potassium bromide is the same as for sodium chloride. Estimate the length of the edge of the unit cell in potassium bromide.

Calculate the interplanar spacings (in picometers) that correspond to diffracted beams of \(X\) rays at \(\theta=20.0^{\circ}\), \(27.4^{\circ},\) and \(35.8^{\circ},\) if the \(X\) rays have a wavelength of \(141 \mathrm{pm}\). Assume that \(n=1\).

Rubidium chloride has the rock salt structure. Cations and anions are in contact along the edge of the unit cell, which is \(658 \mathrm{pm}\) long. The radius of the chloride ion is \(181 \mathrm{pm}\). What is the radius of the \(\mathrm{Rb}^{+}\) ion?

Columbium is another name for one of the elements. This element is shiny, soft, and ductile. It melts at \(2468^{\circ} \mathrm{C}\), and the solid conducts electricity. What kind of solid does columbium form?

The following thermochemical equations apply to acetic acid. \(\begin{array}{ll}\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(s) \longrightarrow \mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(l) & \Delta H_{\text {fusion }}=10.8 \mathrm{~kJ} / \mathrm{mol} \\ \mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(l) \longrightarrow \mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(g) & \Delta H_{\text {vaporization }}=24.3 \mathrm{~kJ} / \mathrm{mol}\end{array}\) Use Hess's law to estimate the value for the heat of sublimation of acetic acid in kilojoules per mole.

When warm, moist air sweeps in from the ocean and rises over a mountain range, it expands and cools. Explain how this cooling is related to the attractive forces between gas molecules. Why does this cause rain to form? When the air drops down the far side of the range, its pressure rises as it is compressed. Explain why this causes the air temperature to rise. How does the humidity of this air compare with the air that originally came in off the ocean? Now explain why the coast of California is lush farmland, whereas valleys (such as Death Valley) that lie to the east of the tall Sierra Nevada mountains are arid and dry.

Gold crystallizes with a face-centered cubic unit cell with an edge length of \(407.86 \mathrm{pm}\). Calculate the atomic radius of gold in units of picometers.

Freshly precipitated crystals are usually very small. Over time the crystals tend to grow larger in a process called digestion. How can we use the concept of dynamic equilibrium to explain this phenomenon?

Lubricants, oils, greases, and so on are very important in everyday life. Explain how a lubricant works in terms of intermolecular forces.