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chemistry

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Naming and Writing Formulas for Molecular Compounds

One milligram of gold is worth only about one cent, but one kilogram of gold is worth approximately $12,500. The correct prefix ( milli- or kilo-) makes quite a difference! Prefixes are important in chemistry, too. The prefixes in the name of a binary molecular compound tell you its composition. Objectives: Interpret the prefixes in the names of molecular compounds in terms of their chemical formulasApply the rules for naming and writing formulas for binary molecular compounds

9.3



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Naming Binary Molecular Compounds

Naming Binary Molecular Compounds

What does a prefix in the name of a binary molecular compound tell you about the compound’s composition?

9.3

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Carbon and oxygen combine to form carbon monoxide (CO) and carbon dioxide (CO2), but these two invisible gases are very different.

9.3 Naming Binary Molecular Compounds

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Sitting in a room with small amounts of CO2

in the air would not present any problems. If the same amount of CO were in the room, you could die of asphyxiation. A naming system that distinguishes between these two compounds is needed.


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A prefix in the name of a binary molecular compound tells how many atoms of an element are present in each molecule


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To name binary molecular compounds:

1. Name the elements in the order listed in the formula.

2. Use prefixes to indicate the number of each kind of atom.

3. Omit the prefix mono- when the formula contains only one atom of the first element in the name.

4.The suffix of the name of the second element is -ide.


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> Molecular compounds

Example:

Name the following binary molecular compounds:

1. P2O3

2. CCl4

3. N2O

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> Writing Formulas for BinaryMolecular Compounds

Writing Formulas for Binary Molecular CompoundsHow do you write the formula for a binary molecular compound?

1. Write the symbol of each anion

2. Use the prefix in front of each name to assign a subscript to that particular cation

3. DO NOT CRISSCROSS!

9.3

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Silicon carbide is a hard material like diamond. The name silicon carbide has no prefixes, so the subscripts of silicon and carbon must be one. Thus, the formula for silicon carbide is SiC.

9.3 Writing Formulas for BinaryMolecular Compounds

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> Molecular compounds

Example:

Write the formula for each of the following:

1. Sulfur trioxide

2. Silicon tetrachloride

3. Carbon monoxide


Section Quiz

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Continue to: Launch:

Assess students’ understanding of the concepts in Section 9.3.

9.3 Section Quiz.


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9.3 Section Quiz.

1. Which of the following compounds is named INCORRECTLY?

a. CS2, carbon disulfide

b. BCl3, boron trichloride

c. IF7, iodine heptafluoride

d. PCl5, phosphorus hexachloride


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2. Which of the following molecular compounds is named INCORRECTLY?

a. SbCl3, antimony trichloride

b. C2O5, dicarbon pentoxide

c. CF4, carbon tetrafluoride

d. H3As, hydrogen arsenide

9.3 Section Quiz.


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3. The correct formula for tetraphosphorus trisulfide is

a. P3S4

b. S3P4

c. P4S3

d. S4P3

9.3 Section Quiz.

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