Transcript Ch09 Lesson09_3

9.3 Naming and Writing Formulas
for Molecular Compounds
>
Chapter 9
Chemical Names and Formulas
9.1 Naming Ions
9.2 Naming and Writing Formulas for Ionic
Compounds
9.3 Naming and Writing Formulas for
Molecular Compounds
9.4 Naming and Writing Formulas for Acids and
Bases
9.5 The Laws Governing How Compounds Form
1
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
CHEMISTRY
& YOU
What numerical
prefixes are used
in chemistry?
The word triathlon
contains the prefix
tri-, indicating the
number 3. Prefixes
are used in
chemistry, too.
2
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
Binary Molecular Compounds
What guidelines are used to write the
name and formula of a binary molecular
compound?
3
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
• Recall that binary ionic compounds are
composed of the ions of two elements, a
metal and a nonmetal.
• Binary molecular compounds are also
composed of two elements, but both
elements are nonmetals and are not ions.
• Binary molecular compounds are
composed of molecules, not ions, so
ionic charges cannot be used to write
formulas or to name them.
4
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
• When two nonmetallic elements combine,
they often do so in more than one way.
• For example, the elements carbon and
oxygen combine to form two gaseous
compounds, CO and CO2.
• It might seem satisfactory to call both of
these compounds carbon oxide.
5
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
• However, the two carbon oxides, CO and
CO2, are very different compounds.
• You exhale CO2 as a product of your
body chemistry, and it is normally present
in the air you breathe.
• CO is a poisonous gas that interferes
with your blood’s ability to carry oxygen
to body cells.
6
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
When you exhale underwater, bubbles
containing CO2 rise to the surface of the water.
7
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
Naming Binary Molecular Compounds
Prefixes in the names
of binary molecular
compounds help
distinguish
compounds
containing different
numbers of atoms,
such as CO and CO2.
8
Prefixes Used in Naming Binary
Molecular Compounds
Prefix
Number
mono-
1
di-
2
tri-
3
tetra-
4
penta-
5
hexa-
6
hepta-
7
octa-
8
nona-
9
deca-
10
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
Naming Binary Molecular Compounds
• Prefixes in the names of binary molecular
compounds tell how many atoms of an
element are present in each molecule of
the compound.
• The prefix mono- would be used for
the single oxygen atom in CO.
• The prefix di- would be used for the
two oxygen atoms in CO2.
9
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
CHEMISTRY
& YOU
How does a triathlon differ from a
pentathlon? How does phosphorus
trifluoride differ from phosphorus
pentafluoride?
10
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
CHEMISTRY
& YOU
How does a triathlon differ from a
pentathlon? How does phosphorus
trifluoride differ from phosphorus
pentafluoride?
A triathlon is composed of 3 sports, while a
pentathlon is composed of 5. Phosphorus
trifluoride is a binary molecular compound that
has 1 phosphorus and 3 fluoride atoms, while
phosphorus pentafluoride contains 1
phosphorus and 5 fluoride atoms.
11
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
Naming Binary Molecular Compounds
• Use the prefixes listed in the table along
with the guidelines on the next slides to
name a binary molecular compound.
• Before you apply these steps, you must
confirm that the compound is a binary
molecular compound.
12
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
To name a binary molecular compound,
use the following guidelines.
1. Write the names of the elements in the order
listed in the formula.
13
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
To name a binary molecular compound,
use the following guidelines.
1. Write the names of the elements in the order
listed in the formula.
2. Use prefixes appropriately to indicate the
number of each kind of atom.
14
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
To name a binary molecular compound,
use the following guidelines.
1. Write the names of the elements in the order
listed in the formula.
2. Use prefixes appropriately to indicate the
number of each kind of atom.
If just one atom of the first element is in the
formula, omit the prefix mono- for that element.
Also, the vowel at the end of a prefix is
sometimes dropped when the name of the
element begins with a vowel.
15
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
To name a binary molecular compound,
use the following guidelines.
1. Write the names of the elements in the order
listed in the formula.
2. Use prefixes appropriately to indicate the
number of each kind of atom.
If just one atom of the first element is in the
formula, omit the prefix mono- for that element.
Also, the vowel at the end of a prefix is
sometimes dropped when the name of the
element begins with a vowel.
3. End the name of the second element with the
suffix -ide.
16
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
Naming Binary Molecular Compounds
• Following these guidelines, CO is named
carbon monoxide and CO2 is named carbon
dioxide.
• Cl2O8 consists of two chlorine atoms and
eight oxygen atoms.
• The name is therefore dichlorine
octoxide.
17
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Sample Problem 9.6
Naming Binary Molecular
Compounds
Name the following binary molecular
compounds.
a. N2O
b. PCl3
18
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Sample Problem 9.6
1 Analyze Identify the relevant concepts.
Confirm that the compound is a binary molecular
compound—a compound composed of two
nonmetals. To name the compound, name the
elements in the order written in the formula. Use
prefixes as necessary to indicate the number of
each kind of atom. Use the suffix -ide on the
name of the second element.
19
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Sample Problem 9.6
2 Solve Apply the concepts to this problem.
Identify the elements in the compound and the
number of atoms of each element in a molecule
of the compound.
a. N2O is composed of two nonmetals,
nitrogen and oxygen.
b. PCl3 is composed of two nonmetals,
phosphorus and chlorine.
20
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Sample Problem 9.6
2 Solve Apply the concepts to this problem.
Write the names of the elements in the order they
are written in the formula. Include prefixes to
show how many atoms of each element. Use the
suffix -ide with the name of the second element.
a. Each molecule of N2O has:
2 nitrogen atoms;
1 oxygen atom.
N2O is dinitrogen monoxide.
21
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Sample Problem 9.6
2 Solve Apply the concepts to this problem.
Write the names of the elements in the order they
are written in the formula. Include prefixes to
show how many atoms of each element. Use the
suffix -ide with the name of the second element.
b. Each molecule of PCl3 has:
1 phosphorus atom;
3 chlorine atoms.
PCl3 is phosphorus trichloride.
22
The prefix
mono- is not
used with the
first element
indicated in
the formula.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
Writing Formulas for Binary Molecular
Compounds
To write the formula of a binary
molecular compound, first use the
prefixes in the name to tell you the
subscript of each element in the
formula. Then, write the correct
symbols for the two elements with the
appropriate subscripts.
23
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Binary Molecular
Compounds
Writing Formulas for Binary Molecular
Compounds
• An interesting example is tetraphosphorus
trisulfide, which is used in some matches.
• The name tetraphosphorus trisulfide has
the prefixes tetra- and tri-, so the subscripts
of phosphorus and sulfur must be 4 and 3,
respectively.
• Thus, the formula for tetraphosphorus
trisulfide is P4S3.
24
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Sample Problem 9.7
Writing Formulas for Binary Molecular
Compounds
Write formulas for the following binary
molecular compounds.
a. nitrogen trifluoride
b. disulfur dichloride
Note: The number 1 is never used
as a subscript in a formula.
25
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Sample Problem 9.7
1 Analyze Identify the relevant concepts.
The prefixes in the name indicate the subscript
of each element in the formula. Write the
symbols for the two elements with the
appropriate subscripts.
26
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Sample Problem 9.7
2 Solve Apply the concepts to this problem.
Use the prefixes to determine how many atoms of
each element are in the compound.
a. Each molecule of
nitrogen trifluoride
has:
1 nitrogen atom; 3
fluorine atoms.
27
b. Each molecule of
disulfur dichloride has:
2 sulfur atoms; 2
chlorine atoms.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
Sample Problem 9.7
2 Solve Apply the concepts to this problem.
Construct the formula using the correct symbols
and subscripts.
a. 1 nitrogen atom; 3
fluorine atoms
NF3
28
b. 2 sulfur atoms; 2
chlorine atoms
S2Cl2
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
What are binary molecular
compounds composed of? How is
their composition different from
binary ionic compounds?
29
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
What are binary molecular
compounds composed of? How is
their composition different from
binary ionic compounds?
Binary molecular compounds are
composed of two elements, which are
nonmetals and are not ions. Binary ionic
compounds are composed of the ions of
two elements, a metal and a nonmetal.
30
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
> Key Concepts
To name a binary molecular compound,
write the names of the elements in the
order listed in the formula. Use prefixes to
indicate the number of each atom. End the
name of the second element with -ide.
To write the formula of a binary molecular
compound, use the prefixes to determine
the subscript of each element. Write the
symbols for the elements with the
subscripts.
31
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
BIG IDEA
Ionic and molecular compounds differ in
composition—ions form ionic compounds, and
molecules form molecular compounds.
32
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
9.3 Naming and Writing Formulas
for Molecular Compounds
>
END OF 9.3
33
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.