Section 7.3 Names and Formulas for
Ionic Compounds
• Relate a formula unit of an ionic compound to its
composition.
• Write formulas for ionic compounds and oxyanions.
• Apply naming conventions to ionic compounds and
oxyanions.
nonmetal: an element that is generally a gas or a
dull, brittle solid and is a poor conductor of heat and
electricity
Section 7.3 Names and Formulas for
Ionic Compounds (cont.)
formula unit
monatomic ion
oxidation number
polyatomic ion
oxyanion
In written names and formulas for ionic
compounds, the cation appears first,
followed by the anion.
Formulas for Ionic Compounds
(cont.)
• A formula unit represents the simplest
ratio of the ions involved.
• Monatomic ions are one-atom ions.
Formulas for Ionic Compounds
(cont.)
• Oxidation number, or oxidation state, is
the charge of a monatomic ion.
Formulas for Ionic Compounds
(cont.)
• Polyatomic ions are ions made
up of more than one atom.
• Never change subscripts of
polyatomic ions, place in
parentheses and write the
appropriate subscript outside the
parentheses.
Formulas for Ionic Compounds
• Write the symbol for each ion including the
charge, Cation first then Anion.
• Overall charge must equal zero.
– If charges cancel, just write symbols.
– If not, use subscripts to balance charges.
– Subscripts represent the number of ions
of each element in an ionic compound.
• Use parentheses to show more than one
polyatomic ion.
Ionic Compound Formation
Example: Aluminum sulfide
1. Write the formulas for the cation
and anion, including CHARGES!
2. Check to see if charges
are balanced.
3. Balance charges , if necessary,
using subscripts. Use parentheses if
you need more than one of a
polyatomic ion.
3+
Al
2
2S
3
Not balanced!
Example: Zinc hydroxide
1. Write the formulas for the cation
and anion, including CHARGES!
2. Check to see if charges are
balanced.
2+
Zn
3. Balance charges , if necessary,
using subscripts. Use parentheses
if you need more than one of a
polyatomic ion.
( OH- )2
Not balanced!
Example: Magnesium carbonate
1. Write the formulas for the cation
and anion, including CHARGES!
2. Check to see if charges
are balanced.
Mg2+ CO32They are balanced!
Example: Iron(III) chloride
1. Write the formulas for the cation
and anion, including CHARGES!
2. Check to see if charges
are balanced.
3. Balance charges , if necessary,
using subscripts. Use parentheses
if you need more than one of a
polyatomic ion.
Fe3+ Cl-
3
Not balanced!
• potassium chloride
– K+ + Cl-

KCl
• magnesium nitrate
– Mg2+ + NO3-

Mg(NO3)2
• copper(II) chloride
– Cu2+ + Cl-

CuCl2
Ionic Compound Nomenclature (naming)
• Write the name of the Cation followed by
the name of the Anion
• Cations keep their original name
• Change ending of monatomic anions to -ide.
• Polyatomic ions have special names. (learn
them)
• Metals with multiple Charges (oxidation
numbers) have Roman Numerals that
indicate the positive charge on the ion
Names for Ions and Ionic Compounds
• An oxyanion is a polyatomic ion
composed of an element (usually a nonmetal), bonded to one or more oxygen
atoms.
Names for Ions and Ionic Compounds
(cont.)
Names for Ions and Ionic Compounds
(cont.)
Examples
• NaBr
– sodium bromide
• K2CO3
– potassium carbonate
• FeCl3
– iron(III) chloride
Section 7.3 Assessment
Which subscripts would you most likely
use for an ionic compound containing an
alkali metal and a halogen? (Remember,
1 = no written subscript)
A. 1 and 2
D
0%
A
D. 1 and 1
C
C. 2 and 3
A. A
B. B
C. C
0%
0%
0%
D. D
B
B. 2 and 1