Chapter 5

The metal polonium (which was named by Maric Curie after her homeland, Poland) crystallizes in a primitive cubic strucrure, with an atom at each corner of a cubic unit cell. The atomic radius of polonium is \(167 \mathrm{pm}\). Sketch the unit cell and determine (a) the number of atoms per unit cell; (b) the coordination number of an atom of polonium; (c) the length of the side of the unit cell.

Silicon can be doped with small amounts of phosphorus to create a semiconductor used in transistors. (a) Is the alloy interstitial or substitutional? Justify your answer. (b) How do you expect the properties of the doped material to differ from those of pure silicon?

Name two compounds that exist as network solids at room temperature and pressure.

Name at least four clements that, in at least one allotropic form, are network solids.

Account for the following observations in terms of the type and strength of intermolecular forces. (a) The melting point of xenon is \(-112^{\circ} \mathrm{C}\) and that of argon is \(-189^{\circ} \mathrm{C}\). (b) The vapor pressure of diethyl ether \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OC}_{2} \mathrm{H}_{3}\right)\) is greater than that of water. (c) The boiling point of pentane, \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{CH}_{3}\), is \(36.1^{\circ} \mathrm{C}\), whereas that of 2,2 -dimethylpropane (also known as neopentane) is \(9.5^{\circ} \mathrm{C}\).

Classify the following solids as ionic, network, or molecular: (a) quartz, \(\mathrm{SiO}_{2}\); (b) limestone, \(\mathrm{CaCO}_{3}\); (c) dry ice, \(\mathrm{CO}_{2}\); (d) sucrose, \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\); (c) polyethylene, a polymer of repeating \(-\mathrm{CH}_{2} \mathrm{CH}_{2}-\) units.

If the edge length of a foc unit cell of \(\mathrm{Rbl}\) is \(732.6 \mathrm{pm}\), how large must the edge length of a cubic single crystal of Rbl be in order for it to contain \(1.00 \mathrm{~mol}\) RbI?

Aluminum metal has a density of \(2.70 \mathrm{~g} \cdot \mathrm{cm}\) and crystallizes in a lattice with a unit cell edge of \(404 \mathrm{pm}\). (a) What type of cubic unit cell is formed by aluminum? (b) What is the coordination number of aluminum?

An oxide of niobium has a unit cell in which there are oxide ions at the middle of each cdge and niobium atoms at the center of each face. What is the empirical formula of this oxide?

Indicate whether the following statements are true or false: (a) If there is an atom present at the comer of a unit cell, there must be the same type of atom at all the comers of the unit cell. (b) A unit cell must be defined so that there are atoms at the corners. (c) If one face of a unit cell has an atom in its center, then the face opposite that face must also have an atom at its center. (d) If one face of a unit cell has an atom in its center, all the faces of the unit cell must also have atoms at their centers.