Page 26 - Materials Chemistry, Second Edition

CHAPTER 2

SOLID-STATE CHEMISTRY

Of the three states of matter, solids possess the most structural diversity. Whereas
gases and liquids consist of discrete molecules that are randomly distributed due to
thermal motion, solids consist of molecules, atoms, or ions that are statically
positioned. To fully understand the properties of solid materials, one must have a
thorough knowledge of the structural interactions between the subunit atoms, ions,
and molecules. This chapter will outline the various types of solids, including
structural classifications and nomenclature for both crystalline and amorphous
solids. The material in this key chapter will set the groundwork for the rest of this
textbook, which describes a variety of materials classes.

2.1. AMORPHOUS VS. CRYSTALLINE SOLIDS
A solid is a material that retains both its shape and volume over time. If a solid
possesses long range, regularly repeating units, it is classified as a crystalline
material. Crystalline solids are only produced when the atoms, ions, or molecules
have an opportunity to organize themselves into regular arrangements, or lattices.
For example, crystalline minerals found in nature have been formed through many
years of extreme temperature and pressure, or slow evaporation processes. Most
naturally occurring crystalline solids comprise an agglomeration of individual
microcrystalline units; single crystals without significant defects are extremely
rare in nature, and require special growth techniques (see p. 28).
If there is no long-range structural order throughout the solid, the material is
best described as amorphous. Quite often, these materials possess considerable
short-range order over distances of 1–10 nm or so. However, the lack of long-
range translational order (periodicity) separates this class of materials from their
crystalline counterparts. Since the majority of studies have been addressed to
study crystalline solids relative to their amorphous counterparts, there is a common
misconception that most solids are crystalline in nature. In fact, a solid product
generated from many chemical reactions will be amorphous by default, unless special
procedures are used to facilitate molecular ordering (i.e., crystal formation).
Although the crystalline state is more thermodynamically-favorable than the

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