http://www.ck12.org Chapter 8. Ionic and Metallic Bonding
Alloys
Analloyis a mixture composed of two or more elements, at least one of which is a metal. You are probably familiar
with some alloys such as brass and bronze (Figure8.15). Brass is an alloy of copper and zinc. Bronze is an alloy
of copper and tin. Alloys are commonly used in manufactured items because the properties of these metal mixtures
are different, and sometimes more useful, than those of a pure metal. For example, bronze is harder than copper and
more easily cast. Brass is very malleable, and its acoustic properties make it useful for musical instruments.
FIGURE 8.15
Bronze, an alloy of copper and tin, has
been in use since ancient times. The
Bronze Age saw the increased use of
metals rather than stone for weapons,
tools, and decorative objects. Brass, an
alloy of copper and zinc, is widely used in
musical instruments like the trumpet and
trombone.Steels are a very important class of alloys. The many types of steels are primarily composed of iron, with various
amounts of the elements carbon, chromium, manganese, nickel, molybdenum, and boron. Steels are widely used in
building construction because of their strength, hardness, and resistance to corrosion. Most large modern structures
like skyscrapers and stadiums are supported by a steel skeleton (Figure8.16).
Alloys can be one of two general types. In one type, called a substitutional alloy, the various atoms simply replace
each other in the crystal structure. In another type, called an interstitial alloy, smaller atoms such as carbon fit in
between the larger atoms in the crystal packing arrangement.
Lesson Summary
- A metallic bond involves the attraction of stationary metal cations to a surrounding sea of mobile valence
electrons. Metallic bonding directly contributes to properties such as high electrical and thermal conductivity,
malleability, ductility, and luster. - Metal atoms are arranged in regular, orderly patterns that often correspond to various closest packing arrange-
ments for spheres. - Alloys are mixtures of metals. Many alloys are widely used because their properties are often more useful for
certain applications than those of pure metals.