Chapter 11

Predict the order of increasing vapor pressure at a given temperature for the following compounds: a. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) b. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}\) c. \(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) Explain why you chose this order.

Classify each of the following by the type of solid it forms: (a) \(\mathrm{Na}\); (b) \(\mathrm{Fe} ;\) (c) \(\mathrm{B}\); (d) \(\mathrm{H}_{2} \mathrm{O}\); (e) \(\mathrm{KF}\).

Classify each of the following by the type of solid it forms: (a) \(\mathrm{LiCl} ;\) (b) \(\mathrm{BaCl}_{2} ;\) (c) \(\mathrm{BCl}_{3}\); (d) \(\mathrm{CCl}_{4}\); (e) \(\mathrm{NCl}_{3}\).

Classify each of the following solid elements as molecular, metallic, ionic, or covalent network. a. tin, Sn b. germanium, Ge c. sulfur, \(\mathrm{S}_{8}\) d. iodine, \(I_{2}\)

Which of the following do you expect to be molecular solids? a. solid silicon tetrachloride, \(\mathrm{SiCl}_{4}\) b. lithium bromide, \(\mathrm{LiBr}\) c. cadmium, \(\mathrm{Cd}\) d. solid chlorine, \(\mathrm{Cl}_{2}\)

On the basis of the description given, classify each of the following solids as molecular, metallic, ionic, or covalent network. Explain your answers. a. a lustrous, yellow solid that conducts electricity b. a hard, black solid melting at \(2350^{\circ} \mathrm{C}\) to give a nonconducting liquid C. a nonconducting, pink solid melting at \(650^{\circ} \mathrm{C}\) to give an electrically conducting liquid d. red crystals having a characteristic odor and melting at \(171^{\circ} \mathrm{C}\)

Associate each of the solids \(\mathrm{Co}, \mathrm{LiCl}, \mathrm{SiC}\), and \(\mathrm{CH}_{3}\) with one of the following sets of properties. a. A white solid melting at \(613^{\circ} \mathrm{C}\); the liquid is electrically conducting, although the solid is not. b. A very hard, blackish solid subliming at \(2700^{\circ} \mathrm{C}\). C. A yellow solid with a characteristic odor having a melting point of \(120^{\circ} \mathrm{C}\). d. A gray, lustrous solid melting at \(1495^{\circ} \mathrm{C}\); both the solid and liquid are electrical conductors.

Associate each of the solids \(\mathrm{BN}, \mathrm{P}_{4} \mathrm{~S}_{3}, \mathrm{~Pb}\), and \(\mathrm{CaCl}_{2}\) with one of the following sets of properties. a. A bluish white, lustrous solid melting at \(327^{\circ} \mathrm{C}\); the solid is soft and malleable. b. A white solid melting at \(772^{\circ} \mathrm{C}\); the solid is an electrical nonconductor but dissolves in water to give a conducting solution. C. A yellowish green solid melting at \(172^{\circ} \mathrm{C}\). d. A very hard, colorless substance melting at about \(3000^{\circ} \mathrm{C}\).

How many atoms are there in a simple cubic unit cell of an atomic crystal in which all atoms are at lattice points?

How many atoms are there in a body-centered cubic unit cell of an atomic crystal in which all atoms are at lattice points?

Metallic iron has a body-centered cubic lattice with all atoms at lattice points and a unit cell whose edge length is \(286.6 \mathrm{pm} .\) The density of iron is \(7.87 \mathrm{~g} / \mathrm{cm}^{3}\). What is the mass of an iron atom? Compare this value with the value you obtain from the molar mass.

Nickel has a face-centered unit cell with all atoms at lattice points and an edge length of \(352.4 \mathrm{pm}\). The density of metallic nickel is \(8.91 \mathrm{~g} / \mathrm{cm}^{3}\). What is the mass of a nickel atom? From the atomic mass, calculate Avogadro's number.

Copper metal has a face-centered cubic structure with all atoms at lattice points and a density of \(8.93 \mathrm{~g} / \mathrm{cm}^{3}\). Its atomic mass is \(63.5\) amu. Calculate the edge length of the unit cell.

Barium metal has a body-centered cubic lattice with all atoms at lattice points; its density is \(3.51 \mathrm{~g} / \mathrm{cm}^{3}\). From these data and the atomic weight, calculate the edge length of a unit cell.

Gold has cubic crystals whose unit cell has an edge length of \(407.9 \mathrm{pm}\). The density of the metal is \(19.3 \mathrm{~g} / \mathrm{cm}^{3}\). From these data and the atomic mass, calculate the number of gold atoms in a unit cell, assuming all atoms are at lattice points. What type of cubic lattice does gold have?

Chromium forms cubic crystals whose unit cell has an edge length of \(288.5 \mathrm{pm}\). The density of the metal is \(7.20 \mathrm{~g} / \mathrm{cm}^{3}\). Use these data and the atomic mass to calculate the number of atoms in a unit cell, assuming all atoms are at lattice points. What type of cubic lattice does chromium have?

Tungsten has a body-centered cubic lattice with all atoms at the lattice points. The edge length of the unit cell is \(316.5 \mathrm{pm}\). The atomic mass of tungsten is \(183.8\) amu. Calculate its density.

Lead has a face-centered cubic lattice with all atoms at lattice points and a unit-cell edge length of \(495.0 \mathrm{pm}\). Its atomic mass is \(207.2\) amu. What is the density of lead?

Metallic magnesium has a hexagonal close-packed structure and a density of \(1.74 \mathrm{~g} / \mathrm{cm}^{3}\). Assume magnesium atoms to be spheres of radius \(r\). Because magnesium has a close-packed structure, \(74.1 \%\) of the space is occupied by atoms. Calculate the volume of each atom; then find the atomic radius, \(r\). The volume of a sphere is equal to \(4 \pi r^{3} / 3\).

If you leave your car parked outdoors in the winter, you may find frost on the windows in the morning. If you then start the car and let the heater warm the windows, after some minutes the windows will be dry. Describe all of the phase changes that have occurred.

Snow forms in the upper atmosphere in a cold air mass that is supersaturated with water vapor. When the snow later falls through a lower, warm air mass, rain forms. When this rain falls on a sunny spot, the drops evaporate. Describe all of the phase changes that have occurred.

The vapor pressure of benzene is \(100.0 \mathrm{mmHg}\) at \(26.1^{\circ} \mathrm{C}\) and \(400.0 \mathrm{mmHg}\) at \(60.6^{\circ} \mathrm{C}\). What is the boiling point of benzene at \(760.0 \mathrm{mmHg}\) ?

The vapor pressure of water is \(17.5 \mathrm{mmHg}\) at \(20.0^{\circ} \mathrm{C}\) and \(355.1 \mathrm{mmHg}\) at \(80.0^{\circ} \mathrm{C}\). Calculate the boiling point of water at \(760.0 \mathrm{mmHg}\)

Describe the behavior of carbon dioxide gas when compressed at the following temperatures: a. \(20^{\circ} \mathrm{C}\) b. \(-70^{\circ} \mathrm{C}\) c. \(40^{\circ} \mathrm{C}\) The triple point of carbon dioxide is \(-57^{\circ} \mathrm{C}\) and \(5.1 \mathrm{~atm}\), and the critical point is \(31^{\circ} \mathrm{C}\) and \(73 \mathrm{~atm}\).

Describe the behavior of iodine vapor when cooled at the following pressures: a. \(120 \mathrm{~atm}\) b. \(1 \mathrm{~atm}\) c. \(50 \mathrm{mmHg}\) The triple point of iodine is \(114^{\circ} \mathrm{C}\) and \(90.1 \mathrm{mmHg}\), and the critical point is \(512^{\circ} \mathrm{C}\) and \(116 \mathrm{~atm}\).

Describe the formation of hydrogen bonds in propanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH} .\) Represent possible hydrogen bonding structures in propanol by using structural formulas and the conventional notation for a hydrogen bond.

Describe the formation of hydrogen bonds in hydrogen peroxide, \(\mathrm{H}_{2} \mathrm{O}_{2}\). Represent possible hydrogen bonding structures in hydrogen peroxide by using structural formulas and the conventional notation for a hydrogen bond.

Ethylene glycol \(\left(\mathrm{CH}_{2} \mathrm{O} \mathrm{HCH}_{2} \mathrm{OH}\right)\) is a slightly viscous liquid that boils at \(198^{\circ} \mathrm{C}\). Pentane \(\left(\mathrm{C}_{5} \mathrm{H}_{12}\right)\), which has approximately the same molecular weight as ethylene glycol, is a nonviscous liquid that boils at \(36^{\circ} \mathrm{C}\). Explain the differences in physical characteristics of these two compounds.

Pentylamine, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\), is a liquid that boils at \(104^{\circ} \mathrm{C}\) and has a viscosity of \(10 \times 10^{-4} \mathrm{~kg} /(\mathrm{m} \cdot \mathrm{s}) .\) Tri- ethylamine, \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{3} \mathrm{~N}\), is a liquid that boils at \(89^{\circ} \mathrm{C}\) and has a viscosity of about \(4 \times 10^{-4} \mathrm{~kg} /(\mathrm{m} \cdot \mathrm{s}) .\) Explain the differences in properties of these two compounds.

Consider the elements \(\mathrm{Al}, \mathrm{Si}, \mathrm{P}\), and \(\mathrm{S}\) from the third row of the periodic table. In each case, identify the type of solid the element would form.

Decide which substance in each of the following pairs has the lower melting point. Explain how you made each choice. a. magnesium oxide, \(\mathrm{MgO}\); or hexane, \(\mathrm{C}_{6} \mathrm{H}_{14}\) b. 1 -propanol, or ethylene glycol, c. silicon, Si; or sodium, \(\mathrm{Na}\) d. methane, \(\mathrm{CH}_{4}\); or silane, \(\mathrm{SiH}_{4}\)

Iridium metal, Ir, crystallizes in a face-centered cubic (close-packed) structure. The edge length of the unit cell was found by \(x\) -ray diffraction to be \(383.9 \mathrm{pm} .\) The density of iridium is \(22.42 \mathrm{~g} / \mathrm{cm}^{3}\). Calculate the mass of an iridium atom. Use Avogadro's number to calculate the atomic mass of iridium.

The edge length of the unit cell of tantalum metal, Ta, is \(330.6 \mathrm{pm} ;\) the unit cell is body-centered cubic (one atom at each lattice point). Tantalum has a density of \(16.69 \mathrm{~g} / \mathrm{cm}^{3} .\) What is the mass of a tantalum atom? Use Avogadro's number to calculate the atomic mass of tantalum.

Calculate the percent of volume that is actually occupied by spheres in a body-centered cubic lattice of identical spheres. You can do this by first relating the radius of a sphere, \(r\), to the length of an edge of a unit cell, \(l .\) (Note that the spheres do not touch along an edge but do touch along a diagonal passing through the body-centered sphere.) Then calculate the volume of a unit cell in terms of \(r\). The volume occupied by spheres equals the number of spheres per unit cell times the volume of a sphere \(\left(4 \pi r^{3} / 3\right)\)

Calculate the percent of volume that is actually occupied by spheres in a face-centered cubic lattice of identical spheres. You can do this by first relating the radius of a sphere, \(r\), to the length of an edge of a unit cell, \(l .\) (Note that the spheres do not touch along an edge but do touch along the diagonal of a face.) Then calculate the volume of a unit cell in terms of \(r\). The volume occupied by spheres equals the number of spheres per unit cell times the volume of a sphere \(\left(4 \pi r^{3} / 3\right)\).

For the hydrogen halides and the noble gases, we have the following boiling points: \(\begin{array}{ll}\text { Halogen Family, }{\underline{\phantom{xx}}}^{\circ} \mathrm{C} & \text { Noble Gases, }^{\circ} \mathrm{C} \\ \mathrm{HF}, 19 & \mathrm{Ne},-246 \\\ \mathrm{HCl},-115 & \mathrm{Ar},-186 \\ \mathrm{HBr},-67 & \mathrm{Kr},-152 \\\ \mathrm{HI},-35 & \mathrm{Xe},-108\end{array}\) Account for the following: a. The general trend in the boiling points of the hydrides and the noble gases. b. The unusual boiling point of hydrogen fluoride. c. The observation that the hydrogen halides have boiling points that are significantly higher than the noble gases.

Account for the following observations: a. Both diamond and silicon carbide are very hard, whereas graphite is both soft and slippery. b. Carbon dioxide is a gas, whereas silicon dioxide is a highmelting solid.

Greater variation exists between the properties of the first and second members of a family in the periodic table than between other members. Discuss this observation for the oxygen family using the following data. \(\begin{array}{llll} & \text { Boiling } & & \text { Boiling } \\ \text { Element } & \text { Point, }^{\circ} \mathrm{C} & \text { Compound } & \text { Point, }^{\circ} \mathrm{C} \\ \mathrm{O}_{2} & -183 & \mathrm{H}_{2} \mathrm{O} & 100 \\ \mathrm{~S}_{8} & 445 & \mathrm{H}_{2} \mathrm{~S} & -61 \\\ \mathrm{Se}_{8} & 685 & \mathrm{H}_{2} \mathrm{Se} & -42\end{array}\)

Use chemical principles to discuss the following observations: a. \(\mathrm{CO}_{2}\) sublimes at \(-78{ }^{\circ} \mathrm{C}\), whereas \(\mathrm{SiO}_{2}\) boils at \(2200^{\circ} \mathrm{C}\). b. HF boils at \(19^{\circ} \mathrm{C}\), whereas \(\mathrm{HCl}\) boils at \(-85^{\circ} \mathrm{C}\). c. \(\mathrm{CF}_{4}\) boils at \(-128^{\circ} \mathrm{C}\), whereas \(\mathrm{SiF}_{4}\) boils at \(-86^{\circ} \mathrm{C}\).

a. Draw Lewis structures of each of the following compounds: \(\mathrm{LiH}, \mathrm{NH}_{3}, \mathrm{CH}_{4}, \mathrm{CO}_{2}\). b. Which of these has the highest boiling point? Why? C. Which of these has the lowest boiling point? Why? d. Which of these has the next-to-highest boiling point? Why?

Discuss why supercritical carbon dioxide is a nearly ideal solvent.

A gecko's toes have been shown to stick to walls through van der Waals forces. Van der Waals forces also exist between your finger and a wall. Why, then, doesn't your finger stick to the wall in the same way as the gecko's toes?

Although a gecko's toes stick easily to a wall, their toes lift off a surface just as easily. Explain.

Describe the structure of a nematic liquid crystal. How is it similar to a liquid? How is it similar to a crystalline solid?

What properties of nematic liquid crystals are employed in LCD displays?

What properties of water are unusual? How does hydrogen bonding explain some of these unusual properties?

The fact that ice is less dense than the liquid is important to weather and aquatic life. Explain.

You may have seen the statement made that the liquid state is the stable state of water below \(100^{\circ} \mathrm{C}\) (but above \(0{ }^{\circ} \mathrm{C}\) ), whereas the vapor state is the stable state above \(100^{\circ} \mathrm{C}\). Yet you also know that a pan of water set out on a table at \(20^{\circ} \mathrm{C}\) will probably evaporate completely in a few days, in which case, liquid water has changed to the vapor state. Explain what is happening here. What is wrong with the simple statement given at the beginning of this problem? Give a better statement.

Consider the following two compounds: \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH} \quad\) 1-pentanol \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3} \quad\) hexane a. What are the different types of intermolecular forces that exist in each compound? b. One of these compounds has a normal boiling point of \(69^{\circ} \mathrm{C}\), and the other has a normal boiling point of \(138^{\circ} \mathrm{C} .\) What is the normal boiling point of hexane? Explain. C. One of these compounds has a viscosity of \(0.313 \mathrm{~g} /(\mathrm{cm} \cdot \mathrm{s})\) and the other has a viscosity of \(2.987 \mathrm{~g} /(\mathrm{cm} \cdot \mathrm{s}) .\) Assign viscosities to 1 -pentanol and to hexane. d. Consider the compound \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Cl}\). Where do you think the boiling point of this compound might lie: above both 1 -pentanol and hexane, intermediate between these two compounds, or below both of these two compounds?

Consider the following three compounds: $$\mathrm{CH}_{3} \mathrm{CHO}, \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}, \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$$ a. Describe the types of intermolecular forces that you expect to see in each. Explain how you arrived at these types. b. The heats of vaporization of these compounds are (in no particular order): \(25.8 \mathrm{~kJ} / \mathrm{mol}, 38.6 \mathrm{~kJ} / \mathrm{mol}\), and \(19.0 \mathrm{~kJ} / \mathrm{mol}\). What is the heat of vaporization of \(\mathrm{CH}_{3} \mathrm{CHO} ?\) c. If the normal boiling point of \(\mathrm{CH}_{3} \mathrm{CHO}\) is \(21^{\circ} \mathrm{C}\), what is its vapor pressure at \(15^{\circ} \mathrm{C}\) ?