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Section 1: Introduction
In the first human chemistry experiments, people worked with solid materials—food, pottery, and metals—for tools and weapons. When chemistry became a laboratory science in the 18th and 19th centuries, many breakthroughs involved work with gases and liquids. Now we've come full circle to a new era of discoveries about the chemistry of solid materials that started in the 20th century and continues today.
Solid materials come in many forms with a dizzying variety of properties. As one example, orthopedists have developed a new way to mend bones broken so badly that they need surgery. They repair the bones with plates made of a shape memory alloy. Otherwise known as a "memory metal," this alloy possesses the ability to change shape in response to alterations in temperature. In the cold operating room, the surgeon stretches the alloy plate and links it to both ends of the broken bone. Once the repair is sewn up, the patient's body heat causes the metal to flip back to its original unstretched shape. As it does so, the metal pulls the bone ends together to begin the healing process. And once the ends have joined, the metal continues to hold them in place, strengthening the bone during rehabilitation.
Figure 13-1. ENIAC, the First Electronic General-Purpose Computer (1945), and a Modern Smart Phone User
The ENIAC computer weighed more than 30 tons, took up 18 square feet, and consumed 170 kilowatts of power. Today's smart phones, powered by microchips made from high-purity silicon, consume a tiny fraction of as much energy and space, and perform operations in seconds that would have taken days a generation earlier.
© Left: Wikimedia Commons, Public Domain. Author: U.S. Army. Right: Wikimedia Commons, Creative Commons License. Author, PictureYouth.
At Cambridge University in England, chemists have used another new type of solid—electrically conducting plastic—to create flexible solar cells. Clustered together to form curtains and placed over a window, the cells could provide electric power for homes that are not connected to power grids.
Memory metals and electrically conducting polymers are just two examples of important advances in the science and technology of solids. Like the original chemists of the Bronze Age and Iron Age, solid-state chemists are making discoveries that are transforming modern life. Solid materials are central to today's societies at all scales, from the steel beams that hold up bridges and skyscrapers to silicon microchips that have revolutionized the global information industry. (Figure 13-1)
Today, solid-state chemistry is one of the most innovative areas of chemical research, producing advanced materials for many uses. As historian Trevor H. Levere (born 1944) observes, "Chemistry is the only science that now builds or creates much of what it goes on to study, from artificial elements to the latest plastics and the most powerful pharmaceutical chemicals, from fertilizers to microchips."1 Solid-state chemistry intersects with many other scientific fields, including geology, energy storage, and materials science—the study of a material's structure, properties, and performance under various conditions.
Figure 13-2. German Steel Rolling Mill (1983)
Manufacturing steel requires an understanding of phase changes that take place as the steel is heated, cast, and cooled.
© Wikimedia Commons, Creative Commons License. Author: Deutsche Fotothek.
Increasingly, modern societies are demanding materials that not only have unique properties, but also are environmentally benign. To develop new materials with finely tuned properties, scientists constantly seek further understanding of how solids and materials are structured, and how small changes can drastically alter their characteristics.
This unit reviews the features that distinguish solids from liquids and gases, and the types of bonds that hold solids together. We will examine four major types of solids—ionic, covalent-network, molecular, and metallic—and how the forces that hold each group's particles together shape those materials' physical characteristics and performance. Then we will use two well-known processes, blacksmithing and steel manufacturing, to consider how solids can exist in multiple phases. (Figure 13-2) Finally, we will look at two broad categories of modern materials that demonstrate the diversity of solids: metal alloys and both natural and synthetic polymers.
1Trevor H. Levere, Transforming Matter: A History of Chemistry from Alchemy to the Buckyball (Johns Hopkins University Press, 2001), p. 182.