1. 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
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2. What numerical prefixes are used in chemistry?
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.
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3. Binary Molecular Compounds
What guidelines are used to write the name and formula of a binary molecular compound?
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4. 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.
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5. 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.
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6. 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.
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7. Binary Molecular Compounds
When you exhale underwater, bubbles containing CO2 rise to the surface of the water.
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8. 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
Prefixes in the names of binary molecular compounds help distinguish compounds containing different numbers of atoms, such as CO and CO2.
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9. 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.
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10. CHEMISTRY & YOU
How does a triathlon differ from a pentathlon? How does phosphorus trifluoride differ from phosphorus pentafluoride?
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11. 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.
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12. 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.
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13. Binary Molecular Compounds
To name a binary molecular compound, use the following guidelines.
Write the names of the elements in the order listed in the formula.
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14. Binary Molecular Compounds
To name a binary molecular compound, use the following guidelines.
Write the names of the elements in the order listed in the formula.
Use prefixes appropriately to indicate the number of each kind of atom.
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15. Binary Molecular Compounds
To name a binary molecular compound, use the following guidelines.
Write the names of the elements in the order listed in the formula.
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.
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16. Binary Molecular Compounds
To name a binary molecular compound, use the following guidelines.
Write the names of the elements in the order listed in the formula.
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.
End the name of the second element with the suffix -ide.
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17. 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.
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18. Naming Binary Molecular Compounds
Sample Problem 9.6
Naming Binary Molecular Compounds
Name the following binary molecular compounds.
N2O
PCl3
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19. Analyze Identify the relevant concepts.
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. 1
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20. Solve Apply the concepts to this problem.
Sample Problem 9.6
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. 2
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21. Solve Apply the concepts to this problem.
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. 2
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22. Solve Apply the concepts to this problem.
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. 2
The prefix mono- is not used with the first element indicated in the formula.
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23. 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.
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24. 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.
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25. Writing Formulas for Binary Molecular Compounds
Sample Problem 9.7
Writing Formulas for Binary Molecular Compounds
Write formulas for the following binary molecular compounds.
nitrogen trifluoride
disulfur dichloride
Note: The number 1 is never used as a subscript in a formula.
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26. Analyze Identify the relevant concepts.
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. 1
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27. Solve Apply the concepts to this problem.
Sample Problem 9.7
Solve Apply the concepts to this problem.
Use the prefixes to determine how many atoms of each element are in the compound. 2
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.
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28. Solve Apply the concepts to this problem.
Sample Problem 9.7
Solve Apply the concepts to this problem.
Construct the formula using the correct symbols and subscripts. 2
a. 1 nitrogen atom; 3 fluorine atoms
b. 2 sulfur atoms; 2 chlorine atoms
NF3
S2Cl2
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29. What are binary molecular compounds composed of
What are binary molecular compounds composed of? How is their composition different from binary ionic compounds?
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30. What are binary molecular compounds composed of
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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31. 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.
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32. BIG IDEA
Ionic and molecular compounds differ in composition—ions form ionic compounds, and molecules form molecular compounds.
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33. END OF 9.3
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