Mighty
Molecule
Models
Upper-elementary students build molecule models to learn about
important molecules and their properties.
Y
By Tom Brown, Greg Rushton, and Marie Bencomo
ou don’t expect to see fifth graders busily puzzling out the chemical formulas of propane, methanol, and other important molecules. While it might seem unusual for students to be exploring these
concepts in their fifth-grade class, the purpose was not to teach high school chemistry but rather
to explore properties that characterize certain molecules. The students used their newly acquired
knowledge of atoms’ bonding requirements to help them build three-dimensional molecular models. This
engaging lesson was one of several developed as part of the SMATHematics Project: The Wonder of Science,
The Power of Mathematics—a collaborative partnership between Kennesaw State University and two local
school districts that aims to provide elementary teachers with accurate science and math classroom activities
designed to kindle curiosity while building understanding (see Internet Resources). The effort is succeeding—as you can see by the fifth-grade classroom experience described here.
January
2008 33
January
2008 33
For several lessons leading up to the
molecule-building inquiry, Clarkdale
Elementary students had been learning about the basic structure of atoms,
including the form and behavior of
protons, neutrons, and electrons. This
introduction to the subatomic structure
of the atom is part of the fifth-grade
science curriculum that deals with the
nature of matter.
At the start of the exploration, the
fifth-grade teacher Ms. Bencomo reviewed these concepts with a role-play.
Two students stood in front of the class
and pretended they were the parts of a
hydrogen atom. One student acted as
the nucleus and the other as the electron. While one student sat staunchly
in the center, the other student buzzed Students explored molecule configurations with ball-and-stick atomic models.
around in an imaginary orbit. Then two
needs to gain stability. They can also bond with anmore students assumed the role of a second atom, with
other atom of the same kind. In order to keep things
a nucleus and one orbiting electron. Ms. Bencomo
relatively simple at the elementary level, Ms. Bencomo
explained that each of these atoms could bond with
chose not to initiate a deeper discussion of how this
each other in order to become more stable as a unit.
bonding relates to stable (noble gas) electron conShe said that by sharing their only electron with each
figurations (a discussion more appropriate for middle
other, the two atoms could form an attractive bond
school students). She then reminded students that
that would help each atom to become more steady and
when atoms bond with one another, they form subsettled. This was important because groups of steady
stances that we call compounds or molecules.
and stable atoms are needed in nature in order to form
But the notion of atoms joining with each other
the fundamental building blocks of matter. To remedy
can get complicated quickly if we consider that the
the situation, she encouraged one of the students to
92 natural elements can combine to form an almost
suggest that the two atoms share electrons so that both
limitless number of compounds. Fortunately, we can
of them could gain stability. The two “electrons” then
simplify things by focusing our efforts on the chemstarted circling both atoms, moving in a figure-eight
istry of living things. Of the 92 naturally occurring
pattern around both nuclei while trying to show that
elements, only about 25% of them are important to
they were attracted to both at the same time. The stuliving things, and only four elements (carbon, nitrodents were clearly pleased with this simple solution to
gen, oxygen, and hydrogen) make up 95% of all living
the problem.
things. If Ms. Bencomo’s students can understand
how those four elements bond to become stable, they
Bonding Rules
can comprehend a great deal about the chemistry of
Ms. Bencomo told the students that they were going
life. For example, the most important molecule on
to learn about some of the patterns that atoms follow
the planet, water, is formed by a combination of two
when they are together. She explained that elements
hydrogen atoms and one oxygen atom (H 2O).
and the atoms that make them up follow patterns that
To start simply, Ms. Bencomo focused student atstudents can understand. For example, most atoms
tention on a poster that showed the name, symbol,
have less stable configurations when by themselves, so
designated color, and number of bonds needed for
they bond with other atoms in ways that make them
each of the “fabulous four” elements (see the Fabulous
more stable. In addition, each different type of atom
Four table in Figure 1) to be stable. (She explained
(element) has to form a certain number of bonds to
the colors were arbitrarily assigned as an easy way of
become more steady and settled. She explained that
representing the different elements in the models and
two atoms can form one bond (single) or two bonds
drawings the students created.) She briefly explained
(double) and sometimes even three bonds (triple)
and used ball-and-stick atomic models to demonstrate
between them—depending on the total number each
34 Science and Children
Photographs courtesy of the authors
Atoms Role-Play
Mighty Molecule Models
Figure 1.
Mighty Molecule lab sheet.
The Fabulous Four
Element
Hydrogen
Oxygen
Nitrogen
Carbon
Symbol
H
O
N
C
Color
Yellow
Red
Light Blue
Black
Bonds to Get Stable
1
2
3
4
For each molecule, you will be given its common name and the number and type of each atom in the molecule. Your job
as a group is to put the atoms together in a way that will form a stable molecule. When you think you have constructed
a stable molecule, predict what you think the formula of the molecule should be, and draw a sketch of the molecule.
The formula should include the symbol of each element and the number of atoms of each element in your molecule.
You are now ready to build some of the most important molecules on our planet. Remember, for the molecule to be stable,
it must form the proper number of bonds. When you build the molecules, use sticks or springs to represent the bonds. You
can form one bond (single) between two atoms or two bonds (double) and sometimes even three bonds (triple).
Procedure:
Build the following molecules using the ball-and-stick models and then predict the formula for the molecule and
draw a sketch of the molecule.
Name of Molecule
Atoms in Molecule
Actual Formula
Sketch of Molecule
water
2 hydrogen
1 oxygen
H2O
O
ammonia
carbon dioxide
methane (natural gas)
H
H
H
1 nitrogen
3 hydrogen
NH3
1 carbon
2 oxygen
CO2
O=C=O
1 carbon
4 hydrogen
CH4
H
N
H
H
H
H
C
H
oxygen (as found in air)
2 oxygen
nitrogen
(as found in air)
2 nitrogen
methanol
(wood alcohol)
1 carbon
4 hydrogen
1 oxygen
O2
O
O=
N2
N
N=
CH3OH
H
H C O
H
H
propane
3 carbon
8 hydrogen
C3H8
H
H
C
H
H
C H
H C
H
H
January 2008 35
Water was the first molecule
on the sheet, and each group of
three students built the molecule together with the rest of the
class. After doing so, they were
asked to predict the formula
for this molecule. One student
suggested that HOH could be
the formula, and a second suggested the more familiar H 2O.
Ms. Bencomo indicated that
both of these formulas were correct (HOH being the structural
formula and H 2O the molecular
formula) and encouraged students to begin working within
their groups to build and sketch
the remaining molecules.
Without any explicit instrucStudents tried different configurations to decide if their molecules were stable.
tion, each group worked toward
the correct structure for each
how each of the fabulous four needed to bond to gain
molecule by trying different configurations and
stability. For example, to make water a water molecule,
deciding if their molecule was stable. For example,
she used tiny sticks to show how the oxygen atom
when constructing a molecule of carbon dioxide
(needing two bonds) forms a bond with two hydrogen
(CO 2), a common approach was to first model its
atoms (each needing one bond) in order to become a
structure on the structure of water by making a single
stable molecule.
bond from the carbon to each oxygen as shown in
Figure 2. This only results in one bond for each oxyPutting It Together
gen and two bonds for carbon (which needs four),
After the discussion of bonding, Ms. Bencomo anand students soon realized that therefore none of
nounced that they were ready to build some of the most
the atoms were stable. The teacher asked students
important molecules on our planet. She distributed
who didn’t observe this to defend their choice and
a bag to each group of three students that contained
was able to lead them to the conclusion that this
an assortment of each type of atom—hydrogen (yelstructure was unstable because it lacked the number
low), oxygen (red), nitrogen (light blue), and carbon
of bonds it needed. Some groups chose to address
(black)—and some sticks and springs to represent
this shortcoming in their model by simply adding
bonds. She then challenged the students to build eight
another single bond between the two oxygen atoms
common molecules, providing students with the name
(Figure 2, second attempt), but this configuration
of each molecule, the number of each atom in the molonly obeys the stability rules for oxygen—not carecule, and the number of bonds each atom needs. She
bon, so their model needed to be revised. A few
distributed a blank lab sheet (see NSTA Connection)
minutes later, excited hands waved frantically in the
that included the common name, a space to write the
air as the students motioned for the teacher to come
predicted formula, and a space to sketch a model of the
look at their structure. Now the central carbon had
molecule. (See a completed lab sheet in Figure 1.)
two bonds to each oxygen and no bonds between the
Figure 2.
Progression of student attempts at sketching the structure of carbon dioxide.
C
O
C
O
1st attempt
36 Science and Children
O
O
2nd attempt
O
C
O
3rd attempt
Mighty Molecule Models
Figure 3.
Student sketching molecular structure.
Connecting to the Standards
This article relates to the following National Science
Education Standards (NRC 1996):
Content Standards
Grades 5–8
Standard B: Physical Science
•Properties and changes of properties in matter
two oxygen atoms (Figure 2, third attempt). “Look!”
they exclaimed. “Is this right?” Ms. Bencomo asked
them to explain their design, and after the students
defended their structure, she smiled broadly and
congratulated them and their persistence and creativity. Then she directed them to predict the correct
chemical formula using water’s formula (H 2O) as an
example and then to draw the structure using their
colored pencils (Figure 3).
Some of the groups were able to work independently throughout the activity, even when faced
with the ultimate task of constructing a model of
methanol (CH 3 OH), which contains three different types of atoms and six atoms to bond together.
Other groups required occasional support, encouragement, or clarification during the 30-minute
lesson, but none became overwhelmed to the point
of giving up. In predicting the formulas for each
molecule, students frequently wrote them in an
unconventional manner, such as writing O 2 C rather
than the commonly accepted CO 2 . Yet such attempts
represent thoughtful inquiries, and Ms. Bencomo
did not correct their responses. The structure of
the instructional sequence also allowed for open
discourse of ideas within and between groups of
students and for groups to work at their own pace. As
a consequence, there was no need for any corrective
or disciplinary action even though the classroom
was noisy and bustling with activity.
Excitement for Future Science
In reflecting on the lesson, Ms. Bencomo felt that
students were very excited about the opportunity
to build molecules. While she was encouraged at
how well they did overall throughout the activity as
well as on the unit test, she recognized that several
students were confused by the fact that an atom
can form multiple bonds with another atom. She
suggested that next time she would probably do a
little more introduction into why atoms may have
two bonds with the same atom and why they may
only have one, as this was one area where students
struggled. An analysis of student journals revealed
that students recognized the importance of these
molecules, as indicated by Julie, who wrote that
“oxygen is a very important molecule, and carbon
dioxide is too, because oxygen is something you need
to breathe, and carbon dioxide is a gas given off in
breathing.” Perhaps more importantly, the students
expressed their enthusiasm for the lesson, as echoed
by Anna, who reflected, “I had lots of fun learning
about molecules and atoms, and I can’t wait to learn
more.” It is only through such active engagement
that we can hope to inspire more students to pursue
opportunities in the fields of science, technology,
engineering, and mathematics. n
Tom Brown ([email protected]) is an associate professor of science education at Kennesaw State
University in Kennesaw, Georgia. Greg Rushton
is an assistant professor of chemistry at Kennesaw
State University in Kennesaw, Georgia. Marie
Bencomo is a fifth-grade teacher at Clarkdale Elementary School in Austell, Georgia.
Resources
National Research Council (NRC). 1996. National science education standards. Washington, DC: National
Academy Press.
Internet
The SMATHematics Project: The Wonder of Science,
The Power of Mathematics http://webtech.kennesaw.edu/tbrown/SMATH/
SMATH.htm
NSTA Connection
Download a blank student lab sheet at
www.nsta.org/SC0801.
January 2008 37
Mighty molecule student lab sheet.
Mighty Molecule Building
Name
_______________
Most atoms are unstable by themselves, so they bond with other atoms in certain
patterns to become stable. Of the 92 natural elements, only about 25% are
important to living things and only four elements make up about 95% of living
things. If you can understand how these fabulous four elements bond in order to
get stable, then you can comprehend a great deal about the chemistry of all living
things.
The Fabulous Four
Element
Hydrogen
Oxygen
Nitrogen
Carbon
Symbol
H
O
N
C
Color
Yellow
Red
Light Blue
Black
Bonds to Get Stable
1
2
3
4
For each molecule, you will be given its common name and the number and type
of each atom in the molecule. Your job as a group is to put the atoms together in
a way that will form a stable molecule. When you think you have constructed a
stable molecule, predict what you think the formula of the molecule should be,
and draw a sketch of the molecule. The formula should include the symbol of
each element and the number of atoms of each element in your molecule.
You are now ready to build some of the most important molecules on our planet.
Remember, for the molecule to be stable, it must form the proper number of
bonds. When you build the molecules, use sticks or springs to represent the
bonds. You can form one bond (single) between two atoms or two bonds
(double) and sometimes even three bonds (triple).
Procedure: Build the following molecules using the ball-and-stick models and
then predict the formula for the molecule and draw a sketch of the molecule.
Name of Molecule
Atoms in Molecule
2 hydrogen
water
1 oxygen
1 nitrogen
ammonia
carbon dioxide
3 hydrogen
1 carbon
Predicted
Formula
Sketch of Molecule
2 oxygen
methane (natural
gas)
1 carbon
4 hydrogen
oxygen (as found in
air)
2 oxygen
nitrogen (as found in
air)
2 nitrogen
1 carbon
methanol (wood
alcohol)
4 hydrogen
1 oxygen
3 carbon
propane
8 hydrogen
Guiding Questions:
1. Do all the molecules contain only single bonds? Why do you think this is the
case?
2. Do all the molecules have the same shape? Why do you think this is the case?
3. Because carbon (black) is the only element that can form long chains by
bonding to itself over and over, it is the backbone element of all living things.
What is unique about carbon that allows it form these big chains?
4. Two of the molecules (methane and propane) that you made are used by
people to as a fuel (for energy). What do each of these molecules have in
common?