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Chemistry of the Elements 283
19-2 General Properties of Metals
Be Careful!
In compounds, metals are cations. That is, they will have a positive charge. The
cations may be shown with the corresponding anions in solution, or in some
particular problems, only the metal cation may be shown. In both of these cases,
you may see designations such as Al 3 . The metals contained in the leftmost
two columns on the periodic table always form 1 and 2 ions, respectively.
All other columns contain metals that may adopt more than one oxidation
state. Variations in oxidation numbers are prevalent amongst the transition
metals. No oxidation number ever exceeds the number at the top of the column
on the periodic table. The highest oxidation number known for any metal in a
compound is 8.
Metals in their elemental state have no charge. Designations such as Al 3 refer
to the metal in, or from, a compound. If you have a piece of metal, you should
use Al, or possibly Al 0 .
Compounds containing metals must also contain a nonmetal or a polyatomic
anion. There are no compounds found in a general chemistry course where a
compound only contains metals.
Metals react with nonmetals. These reactions are oxidation-reduction reactions.
(See Chapters 4 and 18). Oxidation of the metal occurs in conjunction with
reduction of the nonmetal. In most cases, only simple compounds will form. For
example, oxygen, O 2, reacts with nearly all metals to form oxides (compounds
containing O 2 ). Exceptions are the reaction with sodium where sodium peroxide,
Na 2O 2, forms and the reaction with potassium, rubidium, and cesium
where the superoxides, KO 2, RbO 2, and CsO 2 form.
Metals above hydrogen on the Activity Series will displace hydrogen gas from
acids. When this happens, the metal undergoes oxidation. Metals below hydrogen
will not release hydrogen from acid solutions.
19-3 Band Theory of Conductivity
Metals conduct electricity through conduction bands. Conduction bands arise
from the application of Molecular Orbital theory to multi-atom systems.
(See Chapter 10.) The bonding molecular orbitals and, sometimes, other molecular