9.3 Naming and Writing Formulas for Molecular Compounds
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9.3 Naming and Writing Formulas for Molecular Compounds 1 > Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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
Transcript of 9.3 Naming and Writing Formulas for Molecular Compounds
9.3 Naming and Writing Formulas
for Molecular Compounds
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Chapter 9Chemical 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
9.3 Naming and Writing Formulas
for Molecular Compounds
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What numerical
prefixes are used
in chemistry?
The word triathlon
contains the prefix
tri-, indicating the
number 3. Prefixes
are used in
chemistry, too.
CHEMISTRY & YOU
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for Molecular Compounds
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Binary Molecular Compounds
What guidelines are used to write the
name and formula of a binary molecular
compound?
Binary Molecular
Compounds
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for Molecular Compounds
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• 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.
Binary Molecular
Compounds
9.3 Naming and Writing Formulas
for Molecular Compounds
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• 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.
Binary Molecular
Compounds
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for Molecular Compounds
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• 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.
Binary Molecular
Compounds
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for Molecular Compounds
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When you exhale underwater, bubbles
containing CO2 rise to the surface of the water.
Binary Molecular
Compounds
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for Molecular Compounds
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Prefixes in the names of binary molecular compounds help distinguish compounds containing different numbers of atoms, such as CO and CO2.
Binary Molecular
Compounds
Naming Binary Molecular Compounds
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
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for Molecular Compounds
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• 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.
Binary Molecular
Compounds
Naming Binary Molecular Compounds
9.3 Naming and Writing Formulas
for Molecular Compounds
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How does a triathlon differ from a
pentathlon? How does phosphorus
trifluoride differ from phosphorus
pentafluoride?
CHEMISTRY & YOU
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for Molecular Compounds
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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.
CHEMISTRY & YOU
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• 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.
Binary Molecular
Compounds
Naming Binary Molecular Compounds
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for Molecular Compounds
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To name a binary molecular compound, use the following guidelines.
1. Write the names of the elements in the order listed in the formula.
Binary Molecular
Compounds
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for Molecular Compounds
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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.
Binary Molecular
Compounds
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for Molecular Compounds
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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.
Binary Molecular
Compounds
9.3 Naming and Writing Formulas
for Molecular Compounds
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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.
Binary Molecular
Compounds
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for Molecular Compounds
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• 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.
Binary Molecular
Compounds
Naming Binary Molecular Compounds
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for Molecular Compounds
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Sample Problem 9.6
Naming Binary Molecular
Compounds
Name the following binary molecular
compounds.
a. N2O
b. PCl3
9.3 Naming and Writing Formulas
for Molecular Compounds
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Sample Problem 9.6
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.
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for Molecular Compounds
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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.
Sample Problem 9.6
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for Molecular Compounds
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Sample Problem 9.6
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.
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Sample Problem 9.6
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.
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The prefix
mono- is not
used with the
first element
indicated in
the formula.
9.3 Naming and Writing Formulas
for Molecular Compounds
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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.
Binary Molecular
Compounds
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• 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.
Binary Molecular
Compounds
Writing Formulas for Binary Molecular Compounds
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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.
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Sample Problem 9.7
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.
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for Molecular Compounds
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Solve Apply the concepts to this problem.
Use the prefixes to determine how many atoms of
each element are in the compound.
Sample Problem 9.7
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a. Each molecule of
nitrogen trifluoride
has:
1 nitrogen atom; 3
fluorine atoms.
b. Each molecule of
disulfur dichloride has:
2 sulfur atoms; 2
chlorine atoms.
9.3 Naming and Writing Formulas
for Molecular Compounds
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Solve Apply the concepts to this problem.
Construct the formula using the correct symbols
and subscripts.
Sample Problem 9.7
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a. 1 nitrogen atom; 3
fluorine atomsb. 2 sulfur atoms; 2
chlorine atoms
NF3 S2Cl2
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for Molecular Compounds
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What are binary molecular
compounds composed of? How is
their composition different from
binary ionic compounds?
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for Molecular Compounds
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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.
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for Molecular Compounds
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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.
Key Concepts
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for Molecular Compounds
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Ionic and molecular compounds differ in composition—ions form ionic compounds, and molecules form molecular compounds.
BIG IDEA
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for Molecular Compounds
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END OF 9.3
