Chemistry Reference
In-Depth Information
5. Research ultraviolet radiation. What are the different types of UV
rays? How are they different?
6. What are the harmful effects of ultraviolet radiation?
7. In your model, what did you use to represent oxygen atoms?
chlorine atoms? chemical bonds?
8. If you were to repeat this experiment, how would you improve your
model?
What's Going On?
Two oxygen atoms can form a double bond, sharing two electrons and
creating the relatively stable molecule O
2
. Although O
2
is described as
stable, it can be broken down over time by large amounts of ultraviolet
radiation, creating very reactive single oxygen atoms that are called
free
radicals
. These reactive oxygen atoms attach to O
2
molecules in the
atmosphere, forming ozone. In the atmosphere, ozone absorbs harmful
UVB radiation and converts it to heat. In this way, the layer of ozone in
the upper stratosphere protects the Earth from very harmful radiation.
Although ozone is naturally replenished, the process is slow.
The ozone layer has been damaged by chlorine atoms released from
CFCs, which are very reactive and capable of quickly changing ozone into
O
2
. One chlorine atom can combine with about 100,000 ozone molecules
before it is broken down. Ongoing damage to the ozone layer is being
monitored by scientists. Above Antarctica, a large hole in the ozone layer
has been increasing in size (see Figure 3). Some scientists believe that
the hole occurs above Antarctica because the atmosphere there creates
the ideal environment for the reactions to occur. Ice crystals tend to
catalyze the breakdown of CFCs into reactive chlorine atoms, and the
reaction with ozone is more efficient at cooler temperatures.
Once the effects of CFCs were fully understood, they were largely banned
by 1996, but they had been used by industrialized nations for much of the
20th century. Since chlorine and CFCs are not easily broken down, they
can stay in the stratosphere for about 50 years. This means that it will
take a very long time for the hole in the ozone layer to heal.
Connections
One common misconception is that the hole in the ozone layer is related
to the phenomenon of global warming. Although the hole in the
