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12/1/05
11:16 AM
MAZER
Page 251
Electrical forces act in all directions. Each ion, therefore, attracts
all other nearby ions with the opposite charge. The next illustration
shows how this all-around attraction produces a network of sodium
and chloride ions known as a sodium chloride crystal.
+
–
+ –
–
+
–
+
–
+
–
+
–
+
–
+
–
+
+
–
+
+ –
– +
–
+
–
+
–
Notice how each positive ion is
surrounded by six negative ions.
Each negative ion is surrounded by
six positive ions. This regular
arrangement gives the sodium
chloride crystal its characteristic
cubic shape. You can see this
crystal shape when you look at
table salt crystals through a
magnifying glass.
Ionic bonds form between
all nearby ions of opposite
charge. These bonds make ionic compounds very stable and
their crystals very strong. Sodium chloride crystals have a
cubic shape. Other ionic compounds form crystals with different
regular patterns. The shape of the crystals of an ionic compound
depends, in part, on the ratio of positive and negative ions and the
sizes of the ions.
Names of Ionic Compounds
The name of an ionic compound is based on the names of the
ions it is made of. The name for a positive ion is the same as the name
of the atom from which it is formed. The name of a negative ion is
formed by dropping the last part of the name of the atom and adding
the suffix -ide. To name an ionic compound, the name of the positive
ion is placed first, followed by the name of the negative ion. For example, the chemical name for table salt is sodium chloride. Sodium is the
positive sodium ion and chloride is the negative ion formed from
chlorine.
The cubic shape of
sodium chloride crystals
is a result of how the ions
form crystals.
Therefore, to name the compound with the chemical formula BaI2
First, take the name of the positive metal element: barium.
• Second, take the name of the negative, nonmetal element, iodine,
and give it the ending -ide: iodide.
• Third, combine the two names: barium iodide.
•
Similarly, the name for KBr is potassium bromide, and the name
for MgF2 is magnesium fluoride.
Chapter 8: Chemical Bonds and Compounds 251
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