Whole Body Ozone Chemistry
In this activity, students will play the roles of various atoms and molecules
to help them better understand the formation and destruction of ozone in the
Ozone, a molecule containing three oxygen atoms, is made when UV light breaks
the bonds of oxygen molecules containing two oxygen atoms in the stratosphere.
The single oxygen atom is highly reactive and bonds with another oxygen molecule
By having students play the roles of various atoms and molecules, ideas of
basic chemistry in the atmosphere are made more concrete. For example, pairs
of students can represent diatomic oxygen while a trio is required for ozone.
This illustrates chemical reactions involved in the photochemistry of ozone
production and destruction, along with a catalyst that affects the rate of the
- Students will understand how ozone is formed in the earth's stratosphere
and will be able to explain the importance of stratospheric ozone.
- Students will be able to explain how ozone is destroyed in the stratosphere.
- Students will understand that some chemicals can speed up the breakdown
of ozone in the atmosphere.
- Students will be able to explain why chlorofluorocarbons (CFCs) are destructive
to the ozone layer.
Alignment to National Standards
National Science Education Standards
- Physical Science, Properties and Changes of Properties in Matter, Grades
5 to 8, pg. 154, Item #2: "Substances react chemically in characteristic
ways with other substances to form new substances (compounds) with different
characteristic properties. In chemical reactions, the total mass is conserved.
Substances often are placed in categories or groups if they react in similar
ways; metals is an example of such a group."
- Physical Science, Chemical Reactions, Grades 9 to 12, pg. 179, Item #2:
"Light can initiate many important chemical reactions such as photosynthesis
and the evolution of urban smog."
- Physical Science, Chemical Reactions, Grades 9 to 12, pg. 179, Item #3:
"Radical reactions control many processes such as the presence of ozone
and greenhouse gases in the atmosphere, the burning and processing of fossil
fuels, the formation of polymers, and explosions."
Benchmarks for Science Literacy, Project 2061, AAAS
- The Physical Setting, Structure of Matter, Grades 6 to 8, pg. 78, Item #1:
"All matter is made up of atoms, which are far too small to see directly
through a microscope. The atoms of any element are alike but are different
from atoms of other elements. Atoms may stick together in well-defined molecules
or may be packed together in large arrays. Different arrangements of atoms
into groups compose all substances."
- The Physical Setting, Structure of Matter, Grades 9 to 12, pg. 80, Item
#9: "The rate of reactions among atoms and molecules depends on how often
they encounter one another, which is affected by the concentration, pressure,
and temperature of the reacting materials. Some atoms and molecules are highly
effective in encouraging the interaction of others."
- Grade level: 6 to 9 (Note: care must be taken with the younger grades
to make the atomic concepts simple and clear. You may wish to eliminate the
more complex CFC reactions, for example.)
- Allow a minimum of 30 minutes to run the students through each simulation
and discuss the meaning of each.
- 8 1/2 by 11 sheets of paper or cardboard
- Hole punch
- Magic markers
- Clear red and blue plastic sheets to cover flashlight lens
- String (optional)
Note: As written, this activity requires that students hold hands. Younger
students may not have any problems with this, however, the self-consciousness
of adolescents may hinder the spontaneous movement and physical contact required
for this activity. If you think this will be problematic in your classroom,
cut 12-inch lengths of string for the students to hold to make the 'bonds.'
This activity should be done a step at a time, being sure the students understand
the analogy. Otherwise the analogy may be confusing or more difficult to understand
than the concepts being illustrated. It is essential to stop and discuss after
Part 1: Modeling Oxygen in the Earth's Atmosphere
- Let 5 or 6 pairs of students represent oxygen molecules. Each student should
construct a sign using a piece of paper, writing a large O on it and attaching
a string to go around their neck, indicating they are oxygen atoms.
- Students in each pair should hold hands to simulate the bonding between
the atoms of oxygen in each molecule. Have these pairs of students move about
in a cleared area in the classroom to simulate molecular motion. It is appropriate
for them to bounce off a wall or collide with each other as they move about.
After moving about for a minute or so, stop to discuss what has been demonstrated.
Questions and Observations
- How are the moving pairs of students similar to what occurs in the air in
the room? (Oxygen in the air exists as two atoms to each molecule, and, like
all air molecules, oxygen is constantly in motion.)
- How is it different? (Obviously the pair of students is much larger than
one oxygen molecule. In addition, air has other gasesnitrogen, carbon
dioxide, and other trace gases.)
- What could be done to make the analogy better? (Some suggestions might include
having other students act as nitrogen atoms, carbon dioxide molecules, etc.
To make it more realistic, how many nitrogen molecules ()
should be used for each oxygen molecule ()?
About four, since air contains about 80% nitrogen and 20% oxygen.)
- What is oxygen called if it has two atoms per molecule? (Diatomic oxygen
also known as molecular oxygen. A single O atom is known as atomic oxygen.)
Part 2: Simulating the Formation of Ozone in the Stratosphere
- Repeat the steps under modeling the earth's oxygen, but this time darken
or dim the lights in the room.
- Add a student who, with a flashlight, simulates solar radiation. Place a
clear blue plastic sheet over the lens of the flashlight to represent the
ultraviolet short wavelengths that are involved in the breakup of diatomic
- Let pairs of students representing oxygen begin their motion as before.
When the student with the flashlight shines the light on a pair of students,
the bond between them breaks, and students let go of their partner.
- As the motion continues, these single atoms of oxygen move around until
they bump into a pair of oxygen atoms. Each of the single oxygen atoms combines
with the pair they bump into, forming a group of three oxygen atoms. These
three students hold hands, representing a molecule of ozone.
Questions and Observations
- How is this simulation similar to the way ozone is formed in the stratosphere?
(UV light breaks the bonds on oxygen molecules, and the free oxygen atom combines
with other oxygen molecules to produce ozone.)
- What is oxygen with three atoms per molecule called? (ozone)
- How many molecules of ozone can be formed by the breakup of one molecule
of diatomic oxygen by ultraviolet light? (2)
- Why is ozone formed this way in the stratosphere and not in the air near
the earth's surface? (Much more ultraviolet light exists in the stratosphere
than near the earth's surface.)
Part 3: Demonstrating How Ozone Breaks Down in the Stratosphere
- Have several groups of three students, each representing ozone, move about
the room. Pairs of students representing diatomic oxygen can be added as a
touch of realism.
- This time the lens of the flashlight should be covered with clear red plastic
to represent UV light of a longer wavelength.
- When this light is used to illuminate an ozone molecule, the ozone breaks
up to form a diatomic molecule (a pair of students) and an oxygen atom (single
- This process is repeated by shining the light on a second ozone molecule,
producing another pair of oxygen atoms and another single oxygen atom.
- The two single oxygen atoms should then combine to form a pair of atoms,
or a molecule of diatomic oxygen.
Questions and Observations
- How many molecules of diatomic oxygen are formed from the breakup of two
molecules of ozone? (3)
- How is the breakup of ozone in the stratosphere similar to its formation
there? (Both the formation and breakup of ozone involve UV light, but different
Part 4: An Example of a Chemical that Speeds up the Breakdown of Ozone
Of all the chemicals involved in the breakdown of stratospheric ozone, none
have received more attention than the chlorofluorocarbons, or CFCs. The two
most common are CFC-11 ()
and CFC-12 (). These compounds
can be modeled by letting students represent atoms of carbon (C), chlorine (Cl),
and fluorine (F). For example, a molecule of CFC-11 would be composed of one
student representing a carbon atom, another representing a fluorine atom, and
three students representing three chlorine atoms. The students should hold hands
to demonstrate how atoms are bonded in a molecule.
Graphic of the molecular structure of common CFCs
Questions and Observations
- The CFCs are inert, that is, they do not react with other materials under
most conditions. How can this be demonstrated using groups of students to
represent atoms of different elements? (The CFCs can move around together,
but students should lock elbows, showing that the bonds of these molecules
do not break apart easily.)
- The CFCs that enter the atmosphere at the earth's surface have found their
way into the stratosphere. How can this be demonstrated using students to
play the role of various gases in the air? (The CFCs can gradually move from
the place designated in the classroom as the earth's surface to the place
designated as the stratosphere. More ozone molecules should be in the stratosphere.
The student with the flashlight representing UV should be in the place designated
as the stratosphere.)
Part 5: The Role of Chlorine in the Breakdown of Ozone in the Stratosphere
UV light breaks down CFCs in the stratosphere, releasing chlorine atoms. This
can be demonstrated by having a student with a flashlight shine a light on a
group of students representing a molecule of CFC-11 or CFC-12. Let one student
representing a freed chlorine atom move amidst groups of students representing
ozone. The chlorine is involved in the breakdown of ozone as follows:
Cl + ----> ClO +
ClO + O ----> Cl +
- A student representing chlorine pulls an oxygen atom away from an ozone
molecule to form chloride oxide (ClO).
- The two students representing ClO react with an oxygen atom.
- The two students representing oxygen combine to form an oxygen molecule.
- The student representing chlorine is then free to attack another molecule
- Repeat these steps several times to show the chain reaction.
Questions and Observations
- What is a catalyst? (A chemical that promotes a chemical reaction but is
not used up in the reaction.)
- Does the chlorine act as a catalyst in this reaction? (Yes)
- Why is the involvement of chlorine in the breakdown of ozone called a chain
reaction? (Chlorine can cause the breakdown of many ozone molecules and the
chlorine is not altered or destroyed.)
- Because this is a complex, multistep simulation, it would be difficult
for the teacher to informally observe or question each student during the
activities. We suggest instead that students keep a log of the discussion
questions and answers as they go, to be turned in and evaluated by the teacher.
- Draw an unlabeled set of simple "ball and stick" molecular pictures
on overheads illustrating each of the activities done by the students. Have
students copy the overhead drawings and label each molecule and process.
- Provide gumdrops or clay and toothpicks for students to build the molecular
Modifications for Alternative Learners
- The kinesthetic nature of the lesson will be easily followed by English
Language Limited students, but the connection to the molecular processes may
be difficult. Use overhead illustrations liberally to connect the student
activities to the processes, rather than relying only on voice.
- Students with physical limitations could be given gumdrops or clay and toothpicks
to simulate molecular models.
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