C6e Depletion of the Ozone Layer
• A chlorofluorocarbon (CFC) is an organic molecule containing
___________, _____________ and ___________ atoms.
• They are used as_____________________________________________
• They are banned from being used in the UK because they have lead to the
____________________ (thinning) of the ozone layer.
Higher Describe how scientists’ attitude to CFCs has changed
In the beginning scientists thought CFC’s were great because:
• CFC’s are
• These properties make them ideal for
Later they discovered:
• CFC’s deplete the ozone layer (make it thinner)
• so they banned them from use.
So what have countries done to try and stop the depletion of the ozone layer?
• What is ozone, O3?
• Ozone is a form of oxygen with the formula ______ .
• When UV light shines on CFC’s ______________ atoms are formed
Why do we need ozone?
Increased levels of ultraviolet light can lead to medical problems:
Ozone absorbs ________________ light in the stratosphere
Explain why our health will be affected if there is less ozone?
Higher How exactly does ozone absorb UV light?
It does this in 2 very simple reactions:
1. Ozone absorbs UV light and breaks down into an oxygen atom and an oxygen
2. The oxygen atom and molecule join back together to make ozone:
How is the ozone layer depleted?
• The formation of ___________ atoms in the ________________________
leads to the depletion of the ozone layer
• CFC’s can only be removed very ______________ from the stratosphere
• A covalent bond can break in one of 2 ways:
1. Unevenly to form ions
2. Evenly to form highly reactive free radicals
• Only a small number of chlorine atoms are required because a chain reaction is
The chain of reactions:
1. High in the stratosphere, UV light breaks a C-Cl covalent bond in the CFC
molecule to form free radicals
2. Chlorine free radicals then react with ozone, O3
3. The chlorine oxide molecule, ClO is very reactive and reacts with more ozone
4. The chlorine free radical that has been made goes and reacts with another
ozone molecule and so the chain continues. One CFC molecule can react with a
lot of ozone molecules.
What is a safe alternative to CFC’s?
Hydrocarbons can provide safe alternatives to CFCs
HCFC’s can also be used. They break down in the __________atmosphere before
reaching the ozone layer. They are ________ flammable than CFC’s but
__________ than hydrocarbons.