Year 12 HSC Chemistry. * Is fixed – i.e. closed system for matter, but not energy! * Has many functions * Protection from cosmic rays * Keeping us warm.

Year 12 HSC Chemistry

*Is fixed – i.e. closed system for matter, but not energy!

*Has many functions

*Protection from cosmic rays

*Keeping us warm

*Maintaining our supply of oxygen

*Is a very thin layer of gas

*Is small compared to Earth itself

*The lowest layer

*Home of life

*Home of weather

*Home of pollution – mainly from human impact

*Where planes fly

*Home of the ozone layer

*Where the Concorde once flew

*Where greenhouse gases are

*Where global warming originates

*Humans – industry, transport and domestic farms* Particulates:

carbon, dust and metals

*Gaseous: carbon dioxide, smog, unburnt hydrocarbons, etc.

*Can be natural *Chief source is

volcanic activity

*Wildfires

* Lightning

*Allotrope of oxygen

*Formed naturally

*Oxygen molecule split by UV radiation

*Unstable Oxygen atom forms

*Atom joins with molecule to form ozone

O2 + UV O + O

Spliting of the oxygen molecule by UV light. The oxygen atoms formed are not stable and quickly "attack" other oxygen molecules to form ozone molecules.

O + O2 O3

*Diatomic molecule O2

*Contains double covalent bond

*Gas @ RTP

*Required for life

*Triatomic molecule O3

*Contains double covalent bond + coordinate bond

*Gas @ RTP

*Lethal to life

*This is another name for the unstable oxygen atom

*contains unpaired electrons in its valence shell of electrons.

*This is an extremely unstable configuration,

*radicals quickly react with other molecules or radicals to achieve the stable configuration of 4 pairs of electrons in their valence shell

*A special covalent bond forms

*It is called a co-ordinate covalent bond

*One of the oxygen molecule atoms has to share two of its electrons with the atom

Co-ordinate bond – both e- come from one atom

*Ozone is readily split apart to form oxygen molecules

*This is a natural process occurring in the atmosphere

O3 + O 2 O2

*CFC = chloro fluoro carbons

*CFCs were developed in the early 1930s and are used in a variety of industrial, commercial, and household applications

*Used as coolants for commercial and home refrigeration units, aerosol propellants, electronic cleaning solvents, and blowing agents

*Are compounds of bromine, fluorine and carbon (although, fluorine compounds are not to blame for ozone depletion)

*The halons are used as fire extinguishing agents, both in built-in systems and in handheld portable fire extinguishers

*In 1973 chlorine was found to be a catalytic agent in ozone destruction

*It essentially cleaves the ozone to produce oxygen molecules – see next slide

O3 + Cl O2 + ClO

ClO + O O2 + Cl

As we see, the chlorine atom is used and produced by the reaction. This is similar to recycling chemicals in a reaction - the net result is the reaction is self-perpetuating.

1. Human activity puts chlorides and bromides into the atmosphere.

2. Cold conditions are present in the Polar Regions that allow the accumulation of the CFC’s.

3. Sunlight breaks down the CFC’s. 4. The breakdown products destroy ozone.5. The ozone is broken into oxygen molecules.6. Reduced ozone protection in the

stratosphere.

*The CFC problem may be hard to solve because there are already great quantities of CFCs in the environment.  *CFCs would remain in the stratosphere for

another 100 years even if none were ever produced again *In the Montreal Protocol, 30 nations

worldwide agreed to reduce usage of CFCs and encouraged other countries to do so as well (see next slides)

*The Montreal Protocol was a convention signed in 1987 by many countries to greatly reduce the production and use of CFCs which prevent further damage to the ozone layer.

*Since 1987, further amendments to the protocol have imposed and even greater restrictions on the production and use of potentially damaging compounds.

Since 1987, measurements of Cl compound in the atmosphere have shown a decline.

This graph shows the projections with and without the measures for the reduction of these compounds.

•Ground based methods

•Weather balloon-borne instruments

•Satellite data

•Total Ozone mapping Spectrometer (TOMS)

•Solar Backscatter UV

*Monitoring Ozone

GOME Global Ozone Monitoring Experiment

*Small steps are being taken to reduce CFCs including the use of alternate propellants in:

*Refrigeration units

*Air conditioning units

*Propellants for spray cans

*Using pump action instead of gas propellants

*You bet! In place of CFCs and Halons we now use:

* Two main CFC replacements have been developed. They are called hydrofluoroalkanes (HFAs) or hydrofluorocarbons (HFCs), and contain only carbon, hydrogen and fluorine.

* They are non-flammable and chlorine-free, so they have no impact on the stratospheric ozone layer.

* The downside – these compounds are believed to be significant greenhouse gases

*Hydrocarbons such as Cyclopentane and cyclohexane have been put forth as replacements for coolants

*Nitrogen gas (inert) can be used as a blowing agent for substances like styrofoam

C C

CC

CH

H H

H H

H

H

H

HH

C

C C

C

CC

H

HH

HH

H

H

H

H

H

H

H

cyclopentane

cyclohexane