Chapter 20: Metals and Their Compounds

tion “states” that imply that one of the atoms has entirely
lost one or more electrons and the other atom has
taken full possession of one or more electrons. Ions will
not be formed completely by elements near one another
in the Periodic Table. The smaller nonmetal atom will
pull harder on the electrons than the larger metal atom
does, but the electrons will not leave entirely.
Nevertheless, the pretense that they leave helps us write
down the correct formula, so we keep the concept but
change the name to oxidation number to remind ourselves
that we may not be dealing with completely
formed ions.
In naming these salts, the metal is named first followed
by the nonmetal with its last syllable changed to
-ide: NaCl is sodium chloride, Li 2 O is lithium oxide,
and Al 2 S 3 is aluminum sulfide.
The elements chosen for the preceding examples
usually can have only one oxidation number. Many
other elements have at least two common oxidation
numbers; the name must indicate which is the oxidation
number of interest. One way to do this is to use Roman
numerals in parentheses to indicate the oxidation state
of the metal. For example, FeO would be named
iron(II) oxide, and Fe 2 O 3 would be named iron(III)
oxide.
When two nonmetals are combined, it is not always
clear from the oxidation numbers how many atoms are
in the molecule, so the number of atoms of each element
in the molecule is mentioned using the following prefixes:
mono- for one, di- for two, tri- for three, and
tetra- for four. (Other prefixes are used for higher numbers.)
Some examples are CO, carbon monoxide; CO 2 ,
carbon dioxide; and N 2 O 3 , dinitrogen trioxide.
Summary
Elements can be divided into two categories: metals
and nonmetals. In turn we can divide the types of
chemical bonds into three categories: metals with metals
(metallic bond), metals with nonmetals (ionic bond),
and nonmetals with nonmetals (covalent bond). A distinctive
class of physical characteristics is associated
with each type of bond.
In a solid metal the atoms are so close together that
the orbits of the valence electrons overlap. Because the
outer electrons are so loosely held, they can easily drift
from one orbital to another through the overlapping
regions to any part of the lump of metal. The freedom
of the valence electrons to drift results in the following
properties for metals bound by the metallic bond: good
electrical conductivity, metallic luster, malleability,
good thermal conductivity, high chemical reactivity,
and readiness to form alloys.
It is energetically favorable in metal-nonmetal
reactions for the metal to give up valence electrons to
the nonmetal, thus forming electrically charged ions.
Electrically charged ions with opposite charges are then
attracted to one another and become attached to one
another in an ionic bond. Atoms that have lost electrons
in ionic bonds are said to be in positive oxidation
states. Atoms that have gained electrons in ionic bonds
are said to be in negative oxidation states. The oxidation
states are further characterized by the number of
electrons gained or lost: –1 (for atoms that have gained
one electron), +2 (for atoms that have lost two electrons),
etc.
Ionic compounds of a metal and a nonmetal are
called salts. Salts are generally crystalline solids, transparent,
brittle, white in color (although occasionally
colored), electrically nonconducting as a solid, but conducting
in water solutions or in melted form. These
characteristics can be easily understood in terms of the
nature of the ionic bond.
Bonding between nonmetals (covalent bond) will
be described in the next chapter.
STUDY GUIDE
Chapter 20: Metals and Their Compounds
A. FUNDAMENTAL PRINCIPLES: No new fundamental
principles.
B MODELS, IDEAS, QUESTIONS, OR APPLICA-
TIONS
1. What useful groups are compounds often divided
into?
2. Under what conditions do atoms form metallic
bonds?
3. What are the properties of compounds held in
metallic bonds and why do these compounds have
such properties?
4. Under what conditions do atoms form ionic bonds?
5. What are the simplest rules needed to determine the
primary oxidation states of different atoms?
6. What are the properties of compounds held in ionic
bonds, and why do these compounds have such
properties?
7. What procedure leads to the correct chemical formula
for reactants formed in reactions involving
compounds held together in ionic bonds?
C. GLOSSARY
1. Alloys: Alloys are mixtures of metals. Metals
readily form alloys within certain limits.
2. Brittleness: A characteristic of ionic substances,
such as salts, that readily shatter when struck a
sharp blow.
3. Electrical Conductivity: A measure of the degree
to which a substance conducts an electrical current.
Metals have a high electrical conductivity.
4. Electrical Nonconductivity: A characterization of
ionic substances, such as salts, that do not readily
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