Halogenalkanes and the environment Flashcards
…..(CFC) are well-known halogenalkanes
Chlorofluorocarbons
What elements do Chlorofluorocarbons contain?
They only contain chlorine, fluorine and carbon-all the hydrogens have been replaced.
Name some of the features of chlorofluorocarbons.
They’re very STABLE, VOLATILE, NON-FLAMMABLE and NON-TOXIC.
They’re used a lot - e.g. in FRIDGES, ERSOLS CANS, DRY CLEANING, AIR-CONDITIONING and to make FOAMED POLYMERS - Until scientist realised they were destroying the Ozone layer.
…. Atoms are destroying the ozone layer
Chlorine
What is the purpose of Ozone?
Ozone (O3) in the upper atmosphere acts as a CHEMICAL SUNSCREEN. It absorbs a lot of ULTRAVIOLET RADIATION which can cause sunburn or even skin cancer.
How is Ozone formed?
Ozone is FORMED NATURALLY when an OXYGEN MOLECULE is BROKEN DOWN into TWO FREE RADICALs by ULTRAVIOLET RADIATION. The free radicals ATTACK other oxygen molecules forming OZONE.
What did scientist discover in 1970 and 1980s, about the ozone layer in Antarctica and the Arctic?
In the 1970s and 1980s, scientists discovered that the OZONE LAYER above ANTARCTICA was getting THINNER - in fact, it was decreasing very rapidly.
The Ozone layer over the ARCTIC has been found to be thinning too.
These ‘holes’ in the Ozone layer are bad because they allow more harmful UV RADIATION to reach the Earth.
How do Holes in the ozone appear?
The ‘holes’ are formed because CFC’S in the upper atmosphere absorb UV radiation and split tp form CHLORINE FREE RADICALS.
These free radicals CATALYSE the destruction of Ozone-
they DESTROY OZONE MOLECULES and are then REGENERATED to destroy more OZONE.
One chlorine atom can destroy 10,000 ozone molecules before it forms a stable compound.
…. OXIDES can also break ozone down
NITROGEN
Where are Nitrogen oxides produced?
NO free radicals from NITROGEN OXIDES destroy ozone too. Nitrogen oxides are produced by CAR AND AIRCRAFT ENGINES and THUNDERSTORMS.
NO free radicals affect Ozone in the SAME way as chlorine radicals.
What lead scientists to develop ALTERNATIVES to CFCs?
In the 1970s scientists discovered that CFCs were causing damage to the OZONE LAYER.
The ADVANTAGES of CFCs couldn’t outweigh the environmental problems they were causing, so they were BANNED.
What happened in 1989 that caused CFCs to be banned.
The MONTREAL PROTOCOL of 1989 was an INTERNATIONAL TREATY to phase out the use of CFCs and other ozone-destroying halogen alkanes by the year 2000.
There were a few PERMITTED USES such as medical inhalers and in fire extinguishers used in submarines.
Scientist supported the treaty and worked on finding ALTERNATIVES to CFCs such as HCFCs. What are HCFCs?
HCFCs (HYDROCHLOROFLUOROCARBONS) and HFCs (HYDROFLUOROCARBONS) are being used as temporary alternatives to CFCs until safer products are developed.
Scientist supported the treaty and worked on finding ALTERNATIVES to CFCs such as H….carbons.
Hydrocarbons are also used.
What are the drawbacks to HCFCs?
HCFCs are broken down in the atmosphere in 10-20 years.
They still damage the ozone layer, but their effects are much smaller than CFCs.
