Chapter 20: Metals and Their Compounds

Figure 20.2. Lithium orbital energies split and form many energy levels that are very close together as more and more
atoms are added.
Figure 20.3. Malleability of a metal. (a) Forces applied to a group of metal atoms. (b) The solid deforms, but will
spring back to its original shape if the force is removed. (c) The solid is deformed permanently by layers sliding to new
positions.
drift from one orbital to another through the overlapping
regions to any part of the lump of metal.
The drifting electrons give metals their unique
properties, the most common of which are discussed
below.
1. Electrical conductivity. If electrons are
forced into one end of a piece of metal, they
push other mobile electrons out the other end.
This is the mechanism by which wires carry
electricity and is called electrical conductivity.
2. Metallic luster. The closely spaced energy
levels shown in Figure 20.2 permit metals to
absorb virtually every visible wavelength of
light and many invisible wavelengths. A photon
of almost any energy can find an energy
gap that just fits. However, the atoms do not
keep the photons, but immediately radiate
them back (reflection). If all of the visible
light is reflected, the metal appears silver, or if
it is roughened, it appears white. If some of
the violet and blue light is permanently
absorbed, the metal appears gold or copper
colored. High reflectivity in at least a part of
the visible spectrum confers metallic luster.
3. Malleability. Things like glass shatter when
hit with a hammer, but most metals simply
bend or flatten, particularly if they are hot. For
example, gold can be pounded thinner than
paper (to about a millionth of a centimeter
thickness). This characteristic response to
force is termed malleability. On the microscopic
level, the metal nuclei must slide past
each other into new positions without ever
substantially weakening the metallic bond.
The sea of mobile electrons flows wherever it
is needed to keep the bonds strong during
bending and flattening operations (Fig. 20.3).
4. Thermal conductivity. If thermal energy is
added to a piece of metal, the kinetic energy of
the electrons is increased. The electrons move
rapidly through the metal distributing this
kinetic energy throughout by collisions. Thus,
the whole piece of metal becomes hot much
sooner than an equivalent piece of nonmetal.
This transport of thermal energy is termed
thermal conductivity.
5. Chemical reactivity. The mobile electrons
are easy prey for electron-hungry atoms such
as oxygen, so most metals react easily to form
oxides or other compounds with nonmetals. In
fact, only a few metals (such as gold, silver,
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