Objectives

PSc.2.2.3
–Predict chemical formulas
and names for simple
compounds based on
knowledge of bond formation
and naming conventions.
Naming
Compounds and
Writing Formulas
Systematic Naming
There are too many compounds to
remember the names of them all.
 A compound is made of two or more
elements.
 The name should tell us how many and
what type of atoms.

Types of Compounds

There are two types of compounds: ionic
compounds and molecular (covalent)
compounds.
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.

Charges on Ions:
Oxidation Numbers
1+
2+
3+
3- 2- 1-
Naming Cations
We will use the systematic way.
 For cations, if the charge is always the
same (Group A) just write the name of
the metal.

Naming Cations
Tin and lead can have more than one
type of charge.
 Indicate the charge with Roman
numerals in parenthesis.

Example

Li1+

Li is the symbol for lithium.

Lithium is a Group 1A metal, so the
charge is always the same. Write
the name of the metal.

Li1+ is called the Lithium ion.
Example

Sr2+

Sr is the symbol for strontium.

Strontium is a Group 2A metal, so
the charge is always the same.
Write the name of the metal.

Sr2+ is called the Strontium ion.
Example

Sn2+

Sn is the symbol for tin.

Tin has multiple oxidation numbers.
Write the name of the metal,
indicating the charge with Roman
numerals in parenthesis.

Sn2+ is called the Tin (II) ion.
Example

Pb4+

Pb is the symbol for lead.

Lead is a Group 4A metal, and the
charge is not always the same.
Write the name of the metal,
indicating the charge with Roman
numerals in parenthesis.

Pb4+ is called the Lead (IV) ion.
Problem

Name the following cations.

Ca2+
Calcium ion

Al3+
Aluminum ion

Sn4+
Tin (IV) ion
Writing the Formulas for
Cations
Write the formula for the metal.
 If a Roman numeral is in parenthesis
use that number for the charge.
Indicate the charge with a superscript.

Writing the Formulas for
Cations

If no Roman numeral is given, find the
Group A metal on the periodic table and
determine the charge from the column
number.
Example

Lead (II) ion

Pb is the symbol for lead.

Lead has multiple charges, which is
the reason why the charge with
Roman numerals in parenthesis was
included.

The formula for the lead (II) ion is
Pb2+.
Example

Gallium ion

Ga is the symbol for gallium.

Gallium is a Group 3A metal and its
charge is always the same (3+).

The formula for the gallium ion is
Ga3+.
Problem

Write the formulas for the following
cations.
 Magnesium ion Mg2+

Copper (II) ion
Cu2+

Potassium ion
K1+
Problem

Write the formulas for the following ions.
3+
Al

Aluminum ion

Chromium (VI) ion

Mercury (II) ion
6+
Cr
2+
Hg
Naming Anions
Naming monatomic anions is always the
same.
 Change the element ending to – ide
 Example: F1 F is the symbol for fluorine, F1- is
fluor ine.
ide.

Example

Cl1
Cl is the symbol for chlorine.

Chlorine is a Group 7A nonmetal, so
the charge is always the same (1-).

Cl1- is called the chloride ion.
Example

O2
O is the symbol for oxygen.

Oxygen is a Group 6A nonmetal, so
the charge is always the same (2-).

O2- is called the oxide ion.
Problem

Name the following anions.

S2-
sulfide ion

Br1-
bromide ion

N3-
nitride ion
Problem

Name the following anions.

As3-
arsenide ion

Te2-
telluride ion
Writing the Formulas for
Anions
Write the formula for the nonmetal.
 Find the Group A nonmetal on the
periodic table and determine the charge
from the column number.

Problem

Write the formulas for the following
anions.

iodide ion

phosphide ion
1I
P3-
Problem

Write the formulas for the following
anions.

selenide ion

carbide ion
2Se
C4-
Ionic Compounds
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.

Ionic Compounds
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.

Binary Ionic Compounds
Binary ionic compounds are
composed of a metal bonded with a
nonmetal.
 Name the metal ion using a Roman
numeral in parenthesis if necessary.
 Follow this name with the name of the
nonmetal ion.

Example

Name the following binary ionic
compounds.

NaCl
Sodium chloride

Ca3P2
Calcium phosphide
Example

Name the following binary ionic
compounds.

PbO
Lead (II) oxide

SnBr2
Tin (II) bromide
Problem

Name the following binary ionic
compounds.

PbO2
 AlF3
Lead (IV) oxide
Aluminum fluoride
Problem

Name the following binary ionic
compounds.

KCl
Potassium chloride

Na3N
Sodium nitride
Writing Formulas for Binary
Ionic Compounds

Write the symbol for the metal.
Determine the oxidation number from
either the column number or the Roman
numeral and write it as a superscript to
the right of the metal’s symbol.
Writing Formulas for Binary
Ionic Compounds

To the right of the metal’s symbol, write
the symbol for the nonmetal. Determine
the oxidation number from the column
number and write it as a superscript to
the right of the nonmetal’s symbol.
Writing Formulas for Binary
Ionic Compounds

Example: potassium fluoride
K
1+
F
1-
Writing Formulas for Binary
Ionic Compounds

If the two oxidation numbers add
together to get zero, the formula is a
one-to-one ratio of the elements.
Writing Formulas for Binary
Ionic Compounds

Example: potassium fluoride
1+
K KFF
1-
Writing Formulas for Binary
Ionic Compounds

Example: aluminum sulfide
Al
3+
S
2-
Writing Formulas for Binary
Ionic Compounds

If the two oxidation numbers DO NOT
add together to get zero, you will need
to “criss-cross” the superscripts. These
numbers now become subscripts.
Writing Formulas for Binary
Ionic Compounds

Example: aluminum sulfide
3+
2-
Al 2- S 3+
Writing Formulas for Binary
Ionic Compounds

Omit all positive and negative signs and
omit all 1’s.
Writing Formulas for Binary
Ionic Compounds

Example: aluminum sulfide
AlAl2 2SS3 3
Problem

Write the formulas for the following
binary ionic compounds.

Lithium selenide

Tin (II) oxide
Li2Se
SnO
Problem

Write the formulas for the following
binary ionic compounds.

Tin (IV) oxide

Magnesium fluoride
SnO2
MgF2
Ternary Ionic Compounds
Ternary ionic compounds are
composed of at least 3 elements.
 Name the metal ion, using a Roman
numeral in parenthesis if necessary.
 Follow this name with the name of the
polyatomic ion.

Polyatomic ions
Polyatomic ions are groups of atoms
that stay together and have a charge.
 Examples include:

NO3-1
 Acetate C2H3O2-1
 Hydroxide OH-1
 Nitrate
Ternary Ionic Compounds
There is one polyatomic ion with a
positive oxidation number (NH4+) that
may come first in a compound. Name
the ion.
 Follow this name with the name of the
anion or second polyatomic ion.

Examples

Name the following ternary ionic
compounds.
 Li2CO3
Lithium carbonate
 Al(OH)3
Aluminum hydroxide
Examples

Name the following ternary ionic
compounds.
 (NH4)2CO3
 GaPO4
Ammonium carbonate
Gallium phosphate
Problems

Name the following ternary ionic
compounds.
 NaNO3
Sodium nitrate
 CaSO4
Calcium sulfate
Writing Formulas for Ternary
Ionic Compounds

Write the symbol for the metal or
ammonium ion. Write the oxidation
number as a superscript to the right of
the metal’s/ammonium ion’s symbol.
Writing Formulas for Ternary
Ionic Compounds

To the right of the metal’s symbol, write
the symbol for the nonmetal or
polyatomic ion. Write the oxidation
number as a superscript to the right of
the nonmetal’s/polyatomic ion’s symbol.
Writing Formulas for Ternary
Ionic Compounds

Example: potassium nitrate
K
1+
NO3
1-
Writing Formulas for Ternary
Ionic Compounds

If the two oxidation numbers add
together to get zero, the formula is a
one-to-one ratio of the elements.
Writing Formulas for Ternary
Ionic Compounds

Example: potassium nitrate
1+
1-
KKNO
NO
33
Writing Formulas for Ternary
Ionic Compounds

Example: aluminum sulfate
Al
3+
SO4
2-
Writing Formulas for Ternary
Ionic Compounds
If the two oxidation numbers DO NOT
add together to get zero, you will need
to “criss-cross” the superscripts. These
numbers now become subscripts.
 Parentheses are to be placed around
polyatomic ions before criss-crossing.

Writing Formulas for Ternary
Ionic Compounds

Example: aluminum sulfate
3+
2-
Al 2- (SO4 ) 3+
Writing Formulas for Ternary
Ionic Compounds

Omit all positive and negative signs and
omit all 1’s.
Writing Formulas for Ternary
Ionic Compounds

Example: aluminum sulfate
Al2(SO4)3
Problems

Write the formulas for the following
ternary ionic compounds.
 Ammonium
chloride NH Cl
4
 Ammonium
(NH4)2S
sulfide
Problems

Write the formulas for the following
ternary ionic compounds.
 Barium
 Lead
nitrate
(II)
carbonate
Ba(NO3)2
PbCO3