Stratospheric Ozone Layer Depletion
Characteristics of Freons
In general, all Freons are carbon compounds containing chlorine, fluorine, and/or bromine. The most common Freon compounds are chlorofluorocarbons or CFCs in particular, CFC-12 (See CFC-12) whose chemical formula is CCl2F2. Freons are used so widely by industry because of their high densities, low boiling points, low viscosity, and low surface tension. In addition, they are easily liquefied making them ideal for use as refrigerants and solvents. All of these properties made Freons a best seller amongst many industries. Also, the properties made them useful in many other areas. Freons are widely used as solvents, propellants, fire extinguishers, and blowing agents.
Before looking any further into the spread of CFCs, it is important to understand why they are so chemically useful. Since CFC-12 is the most widespread, it will serve as a good example of the chemical usefulness of the entire class of chemicals, known as CFCs. From the discussion above, the molecular formula for CFC-12 is CF2Cl2. The name of this compound is dichlorodifluoromethane. To imagine what this would look like in three dimensional space, begin by envisioning a pyramid with a triangle as its base. Place the carbon atom in the center of the triangle with the chlorines and fluorines at the four points. This is known as a tetrahedral configuration.
Each halogen is fighting to draw one electron away from the central carbon atom. At the same time, the carbon holds the electrons in the covalent bonds so it does not lose them. Since fluorine and chlorine are aggressive elements, the bonds which are formed are very strong. The chlorine acts as a stabilizing agent giving even more stability to this molecule.
These strong covalent bonds and added chlorine stability make CFC-12 inert. This means it does not react with other molecules in its surroundings. Besides its chemical inertness, CFC-12 has many other chemical and physical properties that make it ideal for use in many industrial fields. Its boiling point allowed it to be used as a refrigerant eliminating the danger of explosion or toxicity that was associated with ammonia. Also, because it was inert and nontoxic, it could be used to blow foam for formation of containers or insulation. These same properties made it perfect in medical inhalers and aerosol spray cans. Other applications also arose as the other CFCs were produced. The low costs of production coupled with their versatility and widespread appeal helped them to find their way into many industrial operations.
The same property of inertness which makes CFCs so useful in industry would one day prove to be what makes them so dangerous to the planet. Even as CFCs became more widely spread in industry, they were slowly being vented to the atmosphere. At the time this was not seen as bad practice because they were thought to be safe. Unfortunately, CFCs do not naturally biodegrade. As a result, they persist in the atmosphere. Through natural processes, they make their way up into the stratosphere where the real problem begins. From their inception until the mid seventies, however, CFCs where seen as safe, useful, and noncontroversial.
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