7.4. Metallic Bonds http://www.ck12.org
FIGURE 7.13
Positive metal ions and their shared electrons form metallic bonds.Metallic Bonds and the Properties of Metals
Because of their freely moving electrons, metals are good conductors of electricity. Metals also can be shaped
without breaking. They are ductile (can be shaped into wires) and malleable (can be shaped into thin sheets). Metals
have these properties because of the nature of their metallic bonds.
A metallic lattice, like the one inFigure7.13, may resemble a rigid ionic crystal. However, it is much more flexible.
Look atFigure7.14. It shows a blacksmith hammering a piece of red-hot iron in order to shape it. Why doesn’t
the iron shatter, as an ionic crystal would? The ions of the metal can move within the "sea" of electrons without
breaking the metallic bonds that hold them together. The ions can shift closer together or farther apart. In this way,
the metal can change shape without breaking. You can learn more about metallic bonds and the properties of metals
at this URL: http://www.youtube.com/watch?v=ap5pHBWwpu4 (6:12).
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5086Alloys
Metals are useful for many purposes because of their unique properties. However, pure metals may be less useful
than mixtures of metals. For example, iron is not as strong as steel, which is a mixture of iron and small amounts
of carbon. Steel is so strong that it can hold up huge bridges, like the oneFigure7.15. Steel is also used to make
skyscrapers, cargo ships, cars, and trains.
Steel is an example of an alloy. Analloyis a mixture of a metal with one or more other elements. The other elements
may be metals, nonmetals, or both. An alloy is a solid solution. It is formed by melting a metal and dissolving the
other elements in it. The molten solution is then allowed to cool and harden. Several other examples of alloys and
their uses are shown inFigure7.16. You can learn about an amazing alloy called memory wire at the URL below.
If you have braces on your teeth, you may even have this alloy in your mouth!