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9.3 Naming and Writing Formulas for 9.3 Naming and Writing Formulas for Molecular CompoundsMolecular Compounds
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Chapter 9Chemical Names and Formulas
9.1 Naming Ions9.2 Naming and Writing Formulas for Ionic
Compounds
9.3 Naming and Writing Formulas forMolecular Compounds
9.4 Naming and Writing Formulas for Acids and Bases
9.5 The Laws Governing How Compounds Form
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What prefixes are used in chemistry?
The word triathlon contains the prefix tri-, indicating the number 3. Prefixes are used in chemistry, too.
CHEMISTRY & YOUCHEMISTRY & YOU
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Binary Molecular Compounds
What guidelines are used to write the name and formula of a binary molecular compound?
Binary Molecular Binary Molecular CompoundsCompounds
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• Remember 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 Binary Molecular CompoundsCompounds
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• When two nonmetallic elements combine, they often do so in more than one way, like carbon dioxide (CO2) and carbon monoxide (CO).
• These are very different 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 Binary Molecular CompoundsCompounds
Naming Binary Molecular CompoundsPrefixes 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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• 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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Naming Binary Molecular Compounds
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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 have to confirm that the compound is a binary molecular compound.
Binary Molecular Binary Molecular CompoundsCompounds
Naming Binary 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 Binary Molecular CompoundsCompounds
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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 Binary Molecular CompoundsCompounds
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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 Binary Molecular CompoundsCompounds
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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.
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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.
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Naming Binary Molecular Compounds
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Sample Problem 9.6Sample Problem 9.6
Naming Binary Molecular Compounds
Name the following binary molecular compounds.
a. N2O
b. PCl3
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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 9.6Sample Problem 9.6
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Sample Problem 9.6Sample 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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Sample Problem 9.6Sample 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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• 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 Binary Molecular CompoundsCompounds
Writing Formulas for Binary Molecular Compounds
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Sample Problem 9.7Sample 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 9.7Sample Problem 9.7
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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Use the prefixes to determine how many atoms of each element are in the compound.
Sample Problem 9.7Sample Problem 9.7
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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Solve Apply the concepts to this problem.
Construct the formula using the correct symbols and subscripts.
Sample Problem 9.7Sample Problem 9.7
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a. 1 nitrogen atom; 3 fluorine atoms
b. 2 sulfur atoms; 2 chlorine atoms
NF3 S2Cl2
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What are binary molecular compounds composed of? How is their composition different from binary ionic 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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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 ConceptsKey Concepts
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Ionic and molecular compounds differ in composition—ions form ionic compounds, and molecules form molecular compounds.
BIG IDEABIG IDEA
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>>9.3 Questions
1.Binary molecular compounds are composed of ?
2.List the prefixes in increasing order, that represent the numbers 1 thru 8. (Start with mono….)
3.Write the three rules that are used to write the name of a binary molecular compound.
4. Write the formulas for each of these compounds:
a. nitrogen triiodide _____________
b. diphosphorous pentachloride _____________
c. carbon tetrachloride _____________
d. xenon hexaflouride _____________
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>>9.3 Questions (continued)
5. Write the names for each of these compounds:
a. AlF6 ________________
b. PbO ________________
c. Ba3N2 ________________
d. SF6 ________________
e. N2O5 ________________
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