All About Ozone
- 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.
- 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.
- 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.
- 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
- 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
- Student demonstration of the formation of ozone.
- flavoured mini marshmallows (at least two colours are necessary)
- Divide the class into pairs of students.
- Distribute 12 mini marshmallows all same colour (to represent oxygen atoms) and 6-8 toothpicks per pair.
- Ask students to combine the "oxygen atoms" with the toothpicks to create "oxygen molecules."
- 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;
- Allow students sufficient time to experiment with and discuss possible combinations and recombinations of "oxygen atoms."
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