chemistry grade 8

1. Names and Formulas for Ionic Compounds
Lesson 3

2. Focus Question What are the names and formulas of ionic compounds?
New Vocabulary
formula unit
monatomic ion
polyatomic ion
oxyanion

3. Recall

4. An ionic compound is made up of ions
arranged in a repeating pattern.
Ionic compound
It has both cations and anions
positively charged ion (Cation) Ex: sodium ion Na+
negatively charged ion (Anion) Ex: Chloride Cl-

5. Ions
monatomic ion
is a one-atom ion
polyatomic ions
ions made up of more
than one atom

6. monatomic ion
• A monatomic ion is a one-atom ion, such as Mg2+
or Br–
.
Transition metals, which are in groups 3 through 12, and metals in groups 13 and 14 are
not included in Table 7 because they can form several different positive ions.
• The table below
gives the charges
of common
monatomic ions
according to their
location on the
periodic table.

7. • Polyatomic ions are ions made up of more than one atom.
• A polyatomic ion acts as an individual ion in a compound and its charge
applies to the entire group of atoms.
• Each polyatomic ion acts as a single unit and has one charge.
Nitrate ion
(NO3
–
)
Sulfate ion
(SO4
2–
)
The structure of
common
polyatomic ions
Examples:
Polyatomic ion

8. Table 9 list the
formulas and
charges of
common
polyatomic ions

9. • An oxyanion is a polyatomic
ion composed of an element,
usually a nonmetal, bonded
to one or more oxygen
atoms.
• More than one oxyanion
exists for some nonmetals,
such as nitrogen and sulfur.
Oxyanion
The name of an oxyanion
ends with “–ate” or “-ite”

10. Oxyanion
a) The -ite ending indicates one less oxygen atom than
the -ate ending. However, the ending does not tell you
the actual number of oxygen atoms in the ion
b) Hypo- indicates one oxygen less than -ite.
c) Per- indicates one oxygen more than -ate.
d) Adding Hydrogen to the name decreases the charge by
one.

11. Formula Name Formula Name
Ethanoate (acetate) CO3
2–
CN–
Peroxide
Hydroxide CrO4
2–
MnO4
–
Sulfite
Nitrite SO4
2–
NO3
–
bromate ion
Hypochlorite IO3
-
ClO2
–
Phosphite
Chlorate PO4
3–
ClO4
–
Ammonium ion

12. Based on the ion type, Ionic Compounds can be:
Binary ionic compounds
are composed of positively
charged monatomic ions of a
metal and negatively charged
monatomic ions of a nonmetal.
Polyatomic Ionic
Compounds
ionic compounds that
contain polyatomic ions

13. A. Formulas for Polyatomic Ionic Compounds
Write the formula of the
compound formed from the
ammonium ion NH4
+
& oxide
ion O2-
The chemical formula for an ionic compound called a formula unit,
represents the simplest ratio of the ions involved.
The overall charge of a formula
unit is zero because the formula
unit represents the entire crystal,
which is electrically neutral.
NH4
+
NH4
+
O2- (NH4
)2
O

14. 1. Write the symbol of the cation first
then the anion with its charge.
2. Check the charges, if they are
balanced cancel the charges and
get the formula.
3. If they are not balanced, do
criss-cross.
4. Add ( ) around the polyatomic ion as
it is, and then add the appropriate
subscript.
Because a polyatomic ion exists as a unit, never
change subscripts of the atoms within the ion.
NH4
+
O2-
A. Formulas for Polyatomic Ionic Compounds

15. Formula for a Polyatomic Ionic Compound
Problem
A compound formed by calcium ions and phosphate ions is often used in
fertilizers. Write the compound’s formula.
PO4
3-
Ca2+
Ca3
(PO4
)2

16. Solve Additional Practice, B.P. 185

17. B. Naming Polyatomic Ionic Compounds
1. Name the cation followed by the anion.
2. For the polyatomic ion, simply use its
name as it is.
3. For monatomic anions, use the root of
the element name plus the suffix -ide.
4. For monatomic cations, use the element
name.
Write the name of the
following ionic compound:
NaOH
sodium hydroxide
Note: For transition metals and metals on the right side of the periodic table,
which often have more than one ionic, write a Roman numeral in parentheses
after the name of the cation to distinguish between multiple charges of the same
element.

18. B. Naming Polyatomic Ionic Compounds
1. Name the cation followed by the anion.
2. For the polyatomic ion, simply use its
name as it is.
3. For monatomic anions, use the root of
the element name plus the suffix -ide.
4. For monatomic cations, use the element
name.
Write the name of the
following ionic compound:
Fe3
(PO4
)2
Iron (II) phosphate
Note: For transition metals and metals on the right side of the periodic table,
which often have more than one ionic, write a Roman numeral in parentheses
after the name of the cation to distinguish between multiple charges of the same
element.

19. Solve the Worksheet