Section 9.2 - Naming and Writing Formulas for Ionic Compounds
Introduction
• A recipe is a formula for the sauce—a
complete list of ingredients and their
proportions. Chemistry also uses
formulas. Once you know the rules, you
can write the formula for any chemical
compound.
3. Binary Ionic
Compounds
• In the days before the science of chemistry
developed, the person who discovered a new
compound often named it anything he or she
wished.
•
These masks are made of an
ionic compound with the
common name gypsum. This
name does not tell you anything
about the chemical composition
of the compound, though.
It was not uncommon for the name to describe some
property of the substance or its source.
• The French chemist Antoine-Laurent Lavoisier
(1743-1794) determined the composition of
many compounds in his experiments to show
how chemical compounds form.
• As more and more compound were identified,
Lavoisier realized that it was becoming more and
more difficult to memorize all the unrelated
names of the compounds.
• He worked with other chemists to develop a
systematic method for naming chemical
compounds.
Binary Ionic
Compounds (cont.)
Tin(IV) sulfide, or
SnS2, is used in
glazes for
porcelain fixtures
and dishes.
Tin(II) fluoride, or SnF2, is added
to toothpastes to prevent cavities.
• Naming Binary Ionic
Compounds
• A binary compound is composed
of two elements and can be either
ionic or molecular.
• To name any binary ionic
compound, place the cation name
first, followed by the anion name.
•
Hematite, a
common ore of
iron, contains
iron (III) oxide.
The balanced
formula is Fe2O3.
•
•
Recall that the charges for
monatomic ions for representative
elements can be found in the
periodic table.
Charges for transition elements can
be determined by the roman
numeral or Latin name.
Charges for polyatomic ions can be
found in a polyatomic ions table.
9.2
Binary Ionic
Compounds (cont.)
• Writing Formulas for Binary Ionic
Compounds
• Steps for writing the formula from the
name
1. Write the symbol of the cation and then
the anion.
2. Take charges and write above symbols
3. Criss-cross the charges and write as
subscripts.
4. Reduce if possible
9.2
4. Compounds •
With Polyatomic
Ions
Oysters produce
calcium
carbonate to
form their shells
and sometimes
pearls.
Lead (II) sulfate
is an important
component of
an automobile
battery.
Writing formulas for Compounds with
Polyatomic Ions
1. Write the symbol for the cation followed by the
formula for the polyatomic ion.
2. Put charges above symbols
3. Criss-cross charges and write as subscripts
4. Reduce if necessary
5. If you have more than one polyatomic ion in
the formula, it must have parenthesis around
it.
• For example, calcium nitrate is composed of a calcium
cation (Ca2+) and a polyatomic nitrate anion (NO3–).
• In calcium nitrate, two nitrate anions, each with a 1–
charge, are needed to balance the 2+ charge of each
calcium cation.
• The formula for calcium nitrate is Ca(NO3)2.
9.2
Compounds With
Polyatomic Ions
(cont.)
Sodium
hypochlorite
(NaClO) is used as
a disinfectant for
swimming pools.
The metallic
cation in this
compound is
sodium (Na+) so
the polyatomic ion
must be ClO–.
• Naming Compounds with
Polyatomic Ions
• To name a compound containing
a polyatomic ion, state the cation
first and then the anion, just as
you did in naming binary ionic
compounds.
• Do not change the ending of the
polyatomic ion.
• Use roman numerals for
transitional metals with multiple
charges.
END OF SECTION 2