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THE STRINGS OF THE GUITAR played by the musician Ziggy Marley are formed from a core steel string covered with an alloy wire wrap.

980

METALS AND METALLURGY

WHAT'S AHEAD 23.1

Occurrence and Distribution of Metals We begin by examining the occurrence of metals in the lithosphere along with an introduction to metallurgy, which is the technology associated with extracting metals from their natural mineral sources and preparing them for use.

23.2 Pyrometallurgy We see how high temperatures can be used to extract metals from minerals. Such processes play a particularly important role in the production of iron and steel.

23.3

Hydrometallurgy We see how chemical processes that occur in aqueous solutions can be used to separate metals, with an emphasis on gold and aluminum.

23.4 Electrometallurgy We investigate the use of electricity to reduce and refine metals via electrolysis. We also learn the importance of this approach for the production of sodium, aluminum, and copper.

23.5

Metallic Bonding We review the physical properties of metals and then account for them in terms of two models for metallic bonding-the electron-sea model and the molecular-orbital model.

23.6 Alloys We examine three different types of alloys, or metals that contain more than one element: solution alloys, heterogeneous alloys, and intermetallic compounds.

23.7 Transition Metals We examine the physical properties, electron configurations, oxidation states, and magnetic properties of transition metals and their compounds.

23.8 Chemistry of Selected Transition Metals To finish, we take a closer look at the chemistry of three key transition metals: chromium, iron, and copper.

METALS HAVE PLAYED A MAJOR ROLE IN THE DEVELOPMENT OF

and they continue to do so. For example, without the contributions of metallurgy, rock music as we know it would not exist. The strings of the guitar being played in the chapter-opening photograph are the product of complex

CIVILIZATION,

technology. The core of the strings is made of mild steel, varying in hardness and ductility, depending on the type of guitar on which it will be used. The core string is wound with fine wrap wire, composed typically of an alloy of copper and zinc for acoustic guitar use, or stainless steel for electric guitars. Artists can be very passionate about the particular makes and models of strings they use. When we think of metals in everyday applications, we tend to think of iron and aluminum, perhaps also chromium or nickel. But even metals of very low natural abundance play vital roles in modern technology. To illustrate this point, Figure 23.1 T shows the approximate composition of a high-performance jet engine. Notice that iron, long the dominant metal of technology, is not present to any significant extent. In this chapter we will consider the chemical forms in which metallic elements occur in nature and the means by which we obtain metals from these sources. We will also examine how metals bond in solids and see how metals and mixtures of metals, called alloys, are employed in modern technology. Finally, we will look specifically at the properties of transition metals. As we will see, metals have a varied and interesting chemistry.

981

982

CHAPTER 23

Metals and Metallurgy

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