Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
66 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
7
10. For each of the following pairs of ionic compounds, state which
would be expected to have the higher (more negative) lattice
energy.
a. LiF or KBr
b. NaCl or MgS
c. MgO or RbI
7.3 Names and Formulas for Ionic Compounds
The simplest ratio of the ions represented in an ionic compound is
called a formula unit. The overall charge of any formula unit is
zero. In order to write a correct formula unit, one must know the
charge of each ion. The charges of monatomic ions, or ions
containing only one atom, can often be determined by referring to
the periodic table or table of common ions based on group number.
For example, ions of group 1 typically have a charge of 1ϩ. Those
of group 2 have a charge of 2ϩ. Those of group 17 have a charge
of 1Ϫ.
The charge of a monatomic ion is equal to its oxidation
number. The oxidation number, or oxidation state, of an ion in an
ionic compound is numerically equal to the number of electrons that
were transferred to or from an atom of the element in forming the
compound. If the electrons were transferred from the atom, the ion
has a positive oxidation state. If they were transferred to the atom,
the ion has a negative oxidation state. Most transition metals and
metals of groups 13 and 14 can have more than one oxidation
number.
Oxidation numbers can be used to determine the chemical formulas for ionic compounds. If the oxidation number of each ion is
multiplied by the number of that ion present in a formula unit, and
then the results are added, the sum must be zero.
In the formula for an ionic compound, the symbol of the cation
is written before that of the anion. Subscripts, or small numbers
written to the lower right of the chemical symbols, show the numbers of ions of each type present in a formula unit.
66 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
7
10. For each of the following pairs of ionic compounds, state which
would be expected to have the higher (more negative) lattice
energy.
a. LiF or KBr
b. NaCl or MgS
c. MgO or RbI
7.3 Names and Formulas for Ionic Compounds
The simplest ratio of the ions represented in an ionic compound is
called a formula unit. The overall charge of any formula unit is
zero. In order to write a correct formula unit, one must know the
charge of each ion. The charges of monatomic ions, or ions
containing only one atom, can often be determined by referring to
the periodic table or table of common ions based on group number.
For example, ions of group 1 typically have a charge of 1ϩ. Those
of group 2 have a charge of 2ϩ. Those of group 17 have a charge
of 1Ϫ.
The charge of a monatomic ion is equal to its oxidation
number. The oxidation number, or oxidation state, of an ion in an
ionic compound is numerically equal to the number of electrons that
were transferred to or from an atom of the element in forming the
compound. If the electrons were transferred from the atom, the ion
has a positive oxidation state. If they were transferred to the atom,
the ion has a negative oxidation state. Most transition metals and
metals of groups 13 and 14 can have more than one oxidation
number.
Oxidation numbers can be used to determine the chemical formulas for ionic compounds. If the oxidation number of each ion is
multiplied by the number of that ion present in a formula unit, and
then the results are added, the sum must be zero.
In the formula for an ionic compound, the symbol of the cation
is written before that of the anion. Subscripts, or small numbers
written to the lower right of the chemical symbols, show the numbers of ions of each type present in a formula unit.