9.3
Lesson 9.3 Naming and Writing Formulas for Molecular Compounds
Objectives
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Lesson Links
9.3.1 Apply the rules for naming and writing formulas
for binary molecular compounds.
Ch. 9 Core TR: Section 3 Review
Chapter 9 Online Student Edition
9.3 Lesson Overview (PowerPoint file)
Study WB Chapter 9 Lesson 3
Overview/Materials
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Overview
Standard
In this lesson you will cover the guidelines used to write the names and
formulas of binary molecular compounds.
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0.5
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There are no items.
Chemistry & You
Description
Engage
Have students read the Chemistry & You
text on p. 280.
Ask Do you know of any chemicals that use
prefixes in their names? (Sample answers:
carbon dioxide, carbon monoxide) Point out
that these compounds have prefixes
attached to the second component of the
chemical, but that prefixes can also be
attached to the first component as well.
Have students speculate as to what
information the prefixes provide about the
compounds students named at the
beginning of this activity.
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Chapter 9 Online Student
Edition
Activate Prior Knowledge
Description
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Engage
Remind students that, earlier in this course,
they encountered metric prefixes such as
milli-, centi- and -kilo. Point out that both milli and -centi represent fractional amounts,
while kilo- represents a whole number
amount. Explain that, in this lesson,
students will encounter prefixes that
represent small whole numbers.
Binary Molecular Compounds
Description
Explain
Explain how the order of the elements in the
names of most molecular compounds is
established. Point out that ordinarily, the
less electronegative element appears first in
the name. For example, a compound
containing carbon and sulfur is carbon
disulfide (CS2). Tell students that since
carbon is less electronegative than sulfur, it
appears first. Remind students that
electronegativity increases from left to right
on the periodic table and decreases from
top to bottom. Explain that the first element
in the name and formula is the element
further to the left.
Ask In the compound disulfur dichloride,
S2Cl2, why does the sulfur appear first? (
Sulfur is less electronegative than chlorine.)
Explain that for elements in the same
column, the element nearer the bottom of
the table typically appears first, for example,
iodine heptafluoride (IF7).
Binary Molecular Compounds
Description
Explore
Use a class activity to have students convert
the subscripts in a formula to prefixes in the
name.
Have students make a chart with three
columns: element name, number of atoms,
and prefix. Have them fill in the columns for
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N2O and then name the compound. For
example:
Nitrogen: 2: diOxygen: 1: monoThe name is dinitrogen monoxide. Write the
molecular formulas for other compounds
on the board and have students add them to
their charts. Some possibilities are CCl4,
PBr5, and P4S3.
Binary Molecular Compounds
Description
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Explain
Discuss how some families name a male
offspring the same name as his father.
Explain that this is noted by the person's full
name followed by either the word "junior,"
or by the Roman number of his position in
the family. For instance Eric Philip Thomas
Junior indicates that he is the second male
in his family with the name Eric Philip
Thomas; whereas, Eric Philip Thomas V
indicates that he is the fifth male in his
family with this name. Explain that when a
person's name is original to the family,
such as Wyatt Mitchell Thomas, his name is
not followed by a "1st," a Roman numeral I,
or the words "the original." When a number
or a word does not follow a name, then it is
customarily understood that the name is the
first occurrence for a male in a family. Use
this scenario to help explain why the prefix
mono- is not used to indicate one atom of
the first element in a binary molecular
compound. Explain that when a prefix does
not appear on the first element in a binary
compound, it is customarily understood that
there is only one atom. It would be
redundant to add the prefix.
Binary Molecular Compounds
Description
Extend
Remind students that the Mohs scale rates
the hardness of various minerals on a scale
of 0 to 10. Discuss that silicon carbide is a
binary molecular compound that has a Mohs
scale rating of 9.3. Have students research
this compound and what its rating means in
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terms of its utility in industry.
Assess and Remediate
Description
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Evaluate
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Chapter 9 Online Student
Edition
Write each of the following pairs of
compounds on an index card.
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PBr3 and CrBr3
N2O and Na2O
Cl4 and PbI4
P2O3 and Fe2O3
Ask groups of four students to approach
your desk. Have each student select one
card and identify what the two compounds
have in common. (Each pair has one
element in common.) Then have each
student identify which compound in the pair
is a binary molecular compound and which
one is a binary ionic compound and name
each compound.
Then have students complete the 9.3
Lesson Check.
Remediate
Review the guidelines for naming binary
molecular compounds. Then, have
students write the names of the following
compounds: NO, SiO2, N2O4, and ClF3. (
nitrogen monoxide, silicon dioxide,
dinitrogen tetroxide, and chlorine trifluoride)
have students write the formulas for these
compounds: arsenic pentachloride, iodine
tribromide, and tetraphosphorus hexoxide.
(AsCl5, IBr3, and P4O6)
Differentiated Instruction
Description
Struggling Students
Provide students with a copy of Table 9.4,
but include an additional column so students
can write a couple of examples of
compounds for each row. Instruct students
to use the table as a study guide.
Less Proficient Readers
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Content
Study WB Chapter 9
Lesson 3
Content
Ch. 9 Core TR: Section 3
Review
Content
Table 9.4
Have students write out steps for writing
formulas for molecular compounds in their
own words. Encourage them to use
symbols and examples as needed.
Advanced Students
Increasingly large quantities of the binary
molecular compound CO2 are released into
the atmosphere annually by the burning of
fossil fuels. Once in the atmosphere, carbon
dioxide traps infrared energy near Earth's
surface. As a result, some scientists
predict that over time global temperatures
will rise. Ask students to learn more about
global warming and prepare an oral or
written report or a poster that explains the
current understanding or perception of this
topic.
Focus on ELL
Description
Frontload the Lesson
Preview the prefixes in Table 9.4. Ask
student pairs to make a list of familiar words
that use these prefixes. Have each pair
share their words (and meanings) with the
class. Students should add to their list when
another pair states a word that is not on
their list. Have students keep these
examples in mind as they proceed with the
lesson.
My Notes
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Pacing
Content
Study WB Chapter 9
Lesson 3
Content
Ch. 9 Core TR: Section 3
Review
Content
Ch. 9 Core TR:
Vocabulary Review
Homework