Chlorofluorocarbons halogen compounds

Some halogen compounds have been too reactive for the health of people and the planet. They can destroy healthy cells and attack the Earths atmosphere in the same active way that they kill germs or break down wood into paper. For instance, chlorofluorocarbon (or CFC) compounds used to be popular cooling chemicals in refrigerators and air conditioners and in the gas that pushed hairspray and deodorant out of aerosol cans. CFCs are now widely banned because they destroy Earths atmosphere. Chlorine is also part of the insect killer DDT, a dry cleaning fluid, and the compounds called PCBs. All of these products are now banned or used rarely because they have been linked to pollution and health problems like cancer and liver disease. 

Ozone in the stratosphere is depleted by reactions with halogen atoms. Depletion of stratospheric ozone, commonly referred to as the ozone hole, usually occurs over the Earth s cold regions. The main source of chlorine atoms in the stratosphere is photodissociation of chlorofluorocarbon (CFC) compounds,1369 commonly called Freons, e.g. ... 

It should be mentioned that in the atmospheric reservoir gases other than those listed in Table 1 can be found. For the sake of simplicity the atmospheric cycle of these gases will not be presented. However, the effect of different halogen compounds, including anthropogenic chlorofluorocarbons, on the stability of atmospheric ozone layer will be discussed, in relation to the ozone budget. 

The haloalkanes (also called alkyl halides) are alkanes in which at least one hydrogen atom has been replaced by a halogen atom. Although they have important uses, many haloalkanes are highly toxic and a threat to the environment. The haloalkane 1,2-dichlorofluoroethane, CHC1FCH2C1, is an example of a chlorofluorocarbon (CFC), one of the compounds held responsible for the depletion of the ozone layer (see Box 13.3). Many pesticides are aromatic compounds with several halogen atoms. 

Evidence that many of these compounds can have adverse effects on the immune, endocrine and nervous systems and that some are carcinogenic has grown during the last decade. The role of chlorofluorocarbons (CFCs) and of methyl bromide in the ozone layer depletion is well established (ref. 3).It is therefore not surprising that many halogenated derivatives are cast as environmental and health villains by various concerned groups who call for total phase out of chlorine and chlorinated hydrocarbons. 

Chemical Family a group of elements that share similar chemical properties and share the same column in the periodic table, for example, halogens, alkali earth Chirality condition that describes the handedness of a molecule or whether a molecule exists in forms that can be superimposed on each other Chlorofluorocarbons also called CFCs, compounds consisting of chorine, fluorine, and carbon that are responsible for stratospheric ozone destruction Coagulation precipitation or separation from a dispersed state Coefficient of Thermal Expansion measure of the rate at which a substance will expand when heated... 

Current research suggests that chlorofluorocarbons (CFCs) are responsible for destroying ozone in the upper atmosphere. CFCs are simple halogen-containing oiganic compounds manufactured under the trade name Freons. 

Freons (Sections 7.4, 15.9) Chlorofluorocarbons consisting of simple halogen-containing organic compounds that were once commonly used as refiigerants. 

A carbon atom can be bonded to as many as four halogen atoms, so an enormous number of organic halides can exist. Completely fluorinated compounds are known as fluorocarbons or sometimes perfluorocarbons. The fluorocarbons are even less reactive than hydrocarbons. Saturated compounds in which all H atoms have been replaced by some combination of Cl and F atoms are called chlorofluorocarbons or sometimes freons. These compounds were widely used as refrigerants and as propellants in aerosol cans. However, the release of chlorofluorocarbons into the atmosphere has been shown to be quite damaging to the earth s ozone layer. Since January 1978, the use of chlorofluorocarbons in aerosol cans in the United States has been banned, and efforts to develop both controls for existing chlorofluorocarbons and suitable replacements continue. The production and sale of freons have been banned in many countries. 

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