SCISAT-1

All About Ozone

Teacher's Notes

See Fact Sheet - All About Ozone

Includes:

• Background information on the nature, formation and importance of ozone;
• Transparency masters.

Things to Emphasize

Note: It is not expected that students at this level will understand complex chemical reactions. Given graphic representations and concrete demonstrations though, they should be able to understand the basic concepts of how ozone is formed and why it is important.

1. The ozone layer surrounds the Earth in a zone high in the Earth's atmosphere. The abundance of ozone gradually increases as one moves upwards through the Earth's atmosphere, reaching a maximum abundance at an altitude of about 30 km, and then gradually decreases as one moves further upwards through the atmosphere.
2. Ozone is created as a result of a chain of events:
   • A molecule of oxygen absorbs a high energy ultraviolet photon;
   • The oxygen molecule absorbs sufficient energy to break its molecular bond, producing two free oxygen atoms;
   • These free oxygen atoms either re-combine to form a new oxygen molecule or react with other oxygen molecules to produce ozone molecules.
   
   
3. Oxygen molecules are very efficient absorbers of high energy ultraviolet radiation Ozone is an efficient absorber of the middle and lower energy parts of the ultraviolet spectrum (uv-A and uv-B). During this process the energy of the ultraviolet radiation is converted into thermal energy which heats the Earth's stratosphere.

Student Activities

1. Teacher-led discussion of the composition and location of the ozone layer.

   
   The Ozone Layer. The scale in this diagram is greatly
   exaggerated for purposes of illustration
   Transparency Master

2. Teacher explanation of the formation of ozone.

   uv Absorption by Oxygen
   
   The basic mechanism for the synthesis of ozone
   from the photo-dissociation of oxygen molecules
   Transparency Master

3. Student demonstration of the formation of ozone.

Materials

Procedure

1. Divide the class into pairs of students.
2. Distribute 12 mini marshmallows all same colour (to represent oxygen atoms) and 6-8 toothpicks per pair.
3. Ask students to combine the "oxygen atoms" with the toothpicks to create "oxygen molecules."

   

4. Explain that the oxygen molecules have been "attacked" by high energy ultraviolet photons and that they have absorbed enough energy to break themselves apart. The "free" oxygen atoms have two options:
   • recombine to form new oxygen molecules;
   • combine with an oxygen molecule to form an ozone molecule.
   
5. Allow students sufficient time to experiment with and discuss possible combinations and recombinations of "oxygen atoms."