Chemistry - A Molecular Science

Chapter 8 Solid Materials

Molecular solids are composed of molecu

les or atoms that interact only through

intermolecular interactions. These interacti

ons vary considerably from the weakest

dispersion force in He to fairly strong hy

drogen bonds. Consequently, molecular solids

can be solids, liquids, or gases at room conditions.

Atomic radii can be given as the metallic radius, the covalent radius, or the van der

Waals radius. Metallic radii are deduced from

the distance between metal atoms that are

touching in a metallic solid. Covalent rad

ii are defined from bond lengths because the

length of a covalent bond is the sum of the c

ovalent radii of the bound atoms. The van der

Waals radius is one-half of the van der W

aals distance (distance between two adjacent

molecules in the crystal of an element). The spheres used to represent the atoms in space-filling models are based on their van der Waals radii. Thus, a covalent bond can be represented as the contact of two spheres with ra

dii equal to the covalent radii of the atoms

or as the penetration of two spheres with radii equal to the van der Waals radii.

After studying the material presented in this chapter, you should be able to: 1. identify and define unit cells (Section 8.1); 2. draw the sc, bcc and fcc unit cells (Section 8.2); 3. determine the metallic radius of an atom from

the edge length of the unit cell and cell type

(Section 8.2);

4. determine the formula of a substance based on the unit ce

ll occupancy (Section 8.3);

5. determine the coordination num

ber of an atom or ion in a crystal lattice (Section 8.4);

6. explain packing efficiency and why it is impo

rtant and calculate the densit

y of a solid from its

unit cell dimensions (Section 8.5);

7. differentiate between a conductor, a semico

nductor, and an insulator on the basis of their

band structures (Section 8.6);

8. determine the distances between ions in a crystal given their ionic radii and the crystal type

(Section 8.7);

9. differentiate between the sodium chloride and

cesium chloride structures and explain why

one structure would be preferred ov

er the other (Section 8.7);

10.

distinguish between the following forms of carbon: graphite, diamond, buckyball, and nanotubes (Section 8.8 );

11.

describe the diamond and zinc blende struct

ures adopted by several covalent solids

(Section 8.8);

12.

describe the structure and function

of zeolites and clays (Section 8.8);

13.

define the van der Waal

s distance (Section 8.9);

14.

distinguish between covalent and van der Waals radii and determine a bond length from the covalent radii of the atoms (Section 8.9); and

15.

predict relative melting points fr

om the types of solids (Section 8.10).

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