SECTION 3:
COMPOUND NAMES AND
FORMULAS
KEY IDEAS
How are ionic compounds named?
 What do the numerical prefixes used in naming
covalent compounds tell you?
 What does a compound´s empirical formula
indicate?

KEY TERMS
Empirical
formula
Anion
Molecular
formula
Cation
NAMING IONIC COMPOUNDS
The names of ionic compounds consist of the
names of the ions that make up the
compounds
 Name of cations include the elements of which
they are composed

Ion name
and symbol
Ion charge
Cesium
ion, Cs+
Lithium Sodium Barium ion,
ion, Li+ ion, Na+ Ba2+
1+
Calcium
ion, Ca2+
2+
Aluminum
ion, Al3+
3+
NAMING IONIC COMPOUNDS

Names of anions are altered names of elements
 NaF:
is made of sodium ions, Na+, and fluoride ions,
F-. Therefore, its name is sodium fluoride

An ionic compound must have a total charge of
zero
 If
an ionic compound is made up of ions that have
different charges, the ratio will not be 1:1
 For calcium fluoride to have a total charge of zero,
there must be two fluoride ions for every calcium ion
NAMING IONIC COMPOUNDS

Some cation names must show their charge
 The
charge of the iron cation in Fe2O3 is different
from the charge of the iron cation in FeO. In cases
such as this, the cation name must be followed by a
Roman numeral in parentheses that shows the
cation’s charge.
 Fe2O3 is made of Fe3+ ions, so it is named iron (III)
oxide. FeO is made of Fe2+ ions, so it is named iron
(II) oxide.
NAMING IONIC COMPOUNDS

Determine the charge of a transition metal
cation
 How
can you tell that the iron ion in Fe2O3 has a
charge of 3+?

Write formulas for ionic compound using
names
 You
can find the charge of each ion in a compound
if you are given the compound’s formula. You can
find the formula for a compound if you are given the
compound’s name
NAMING IONIC COMPOUNDS

Math Skills: Writing Ionic Formulas
 Go
to go.hrw.com and enter keyword HK8MP
NAMING COVALENT COMPOUNDS
For covalent compounds or two elements,
numerical prefixes tell how many atoms of each
element are in the molecule
 Numerical prefixes are used to name covalent
compounds of two elements

 If
there is only one atom of the first element, the
name does not get a prefix
 The element farther to the right in the periodic
table is named second and ends in –ide
 One boron atom and three fluorine atoms make up
boron trifluoride, BF3
EMPIRICAL FORMULAS
An empirical formula tells us the smallest
whole-number ratio of atoms that are in a
compound
 Different compounds can have same empirical
formula
 Molecular formulas are determined from
empirical formulas
 Masses can be used to determine empirical
formulas

EMPIRICAL FORMULAS
Empirical formula: the composition of a
compound in terms of the relative number and
kinds of atoms in the simplest ratio
 Molecular formula: a chemical formula that
shows the number and kinds of atoms in a
molecule, but not the arrengement of atoms

EMPIRICAL FORMULAS

Math Skills: Finding Empirical Formulas
 Go
to go.hrw.com and enter keyword HK8MP
HOMEWORK