8.3. Metals and Metallic Bonds http://www.ck12.org
heat very well because of their free-flowing electrons. As electrons enter one end of a piece of metal, an equal
number of electrons flow outward from the other end, allowing an electrical current to pass through the material
with minimal resistance. Additionally, because the electron "glue" that holds the metal atoms together is very easy
to deform and reshape, bulk metals can be easily hammered, bent, and pulled without breaking apart.
Types of Metals
Precious Metals
A number of relatively rare metals are quite resistant to corrosion. These metals are sometimes referred to as precious
metals due to their scarcity and their ability to remain pure over time. The exact list varies, but metals that are usually
classified as precious include gold, silver, ruthenium, rhodium, palladium, osmium, iridium, and platinum. Some
precious metals are shown in (Figure8.13). Compared to other metals, precious metals tend to have relatively high
ionization energies and electronegativity values.
FIGURE 8.13
Precious metalsRare Earth Metals
The rare earth metals are a set of seventeen chemical elements (the lanthanide series plus scandium and yttrium)
that have particular importance for a variety of industrial processes and are used frequently in modern technology.
Despite their name, rare earth metals are actually relatively abundant in the earth’s crust. However, the extraction of
many of these metals is quite difficult and has made their supply somewhat limited. They are highly sought after for
this reason.Figure8.14 shows the rare earth metals.
Alloys
In addition to being used in their pure elemental forms, metals can be melted down and combined with other metals
(and sometimes small amounts of nonmetals) to form mixtures known asalloys. The properties of alloys are often
quite different than the properties of the base elements from which they formed. For example, iron is often mixed
with small amounts of carbon or other metals to create steels. By modifying the relative amounts of the added
components, properties like hardness, flexibility, and corrosion resistance can be fine-tuned so that the material is
suitable for a particular application. For example, elemental iron corrodes readily in air and water (seeFigure8.15),
but stainless steel (which is still mostly iron, but contains about 10-12% chromium by mass) resists corrosion to a
large extent. It is used as an exterior building material for extravagant buildings such as that shown inFigure8.16.
Alloys that are mostly composed of mercury are known asamalgams. Amalgams often have special properties that
stem from the fact that mercury exists as a liquid at room temperature. As a result, metal amalgams are used for a
variety of purposes, including dentistry and the extraction of other pure metals such as gold.