Chlorinated Hydrocarbons

Chemistry, the study of matter and its interactions, can be divided broadly into two groups: inorganic chemistry and organic chemistry. Inorganic chemistry is concerned with atoms and molecules that, by and large, do not contain the element carbon. For example, table salt, or sodium chloride (NaCl) is an inorganic compound. The production of table salt and water from the reaction of sodium hydroxide (NaOH) and hydrochloric acid (HCl) is an example of a reaction in inorganic chemistry, since none of the elements within the compounds are carbon. Exceptions to the no-carbon rule are oxides like carbon dioxide, which we exhale when we breathe, and carbonates, like calcium carbonate (blackboard chalk). Although these substances contain carbon, they are considered to be inorganic in nature.

Organic chemistry, then, is the branch of chemistry dealing with most carbon-containing compounds. Carbon, the sixth element listed in the periodic table of elements, is a very versatile element. Atoms of carbon have the capacity to form chemical bonds with other carbon atoms in many configurations. This great variety makes carbon containing, or organic, molecules very important. Most biological molecules involved in the very chemical processes of life and in most of the cellular structures of living things are organic molecules. Approximately 98% of all living things are composed of organic molecules containing the three elements carbon, hydrogen, and oxygen.

Organic molecules vary both in the number of carbon atoms they contain and in the spatial arrangement of the member carbon atoms. Examples of organic molecules containing only one carbon atom are methane (natural gas), chloroform (a general anesthetic), and carbon tetrachloride (an industrial solvent). But most organic molecules contain more than one carbon atom. Like people holding hands, carbon atoms can form molecules that look like chains. The carbon atoms are chemically linked with each other, like people linked together hand-in-hand in a chain.

Some organic molecules are very short chains of three or four carbon atoms. Other organic molecules are very long chains, containing many carbon atoms linked together. Also, just as people in a chain can form a ring when the first person and the last person in the chain join hands, the carbon atoms in an organic molecule can form ring structures, called aromatic rings. The most common rings are five- and six-member rings, containing five or six atoms of carbon respectively.

Hydrocarbons, then, are specific organic molecules that contain only carbon and hydrogen chemically bound together in chains or in rings. Many hydrocarbons are actually combinations of chains and rings, or multiple rings linked together. Also, some hydrocarbons can be branched chains. These carbon chains have portions branching from a main chain, like limbs from the trunk of a tree. The number of carbon atoms involved, and the pattern of chain formation or aromatic ring formation determines the unique chemical and physical properties of particular organic hydrocarbons (like rubber, or plastic, or volatile liquid). Chlorinated hydrocarbons are organic hydrocarbon chains and/or aromatic rings that also contain chlorine atoms chemically linked within the molecule.

Many organic molecules, and many chlorinated hydrocarbons, are actually polymers. Organic polymers are large molecules made of many smaller repeating units joined together. The smaller subunits of polymers are called monomers. Just as a locomotive train is made of many train cars linked together, polymers are many smaller monomers linked together in a line. For example, DNA (deoxyribonucleic acid) in the chromosomes of cells is a polymer of nucleotide monomers. Many repeating nucleotide subunit molecules are joined together to form a large molecule of DNA. Similarly, polystyrene plastic that is used to make foam cups, toys, and insulation, is a hydrocarbon polymer consisting of carbon chains and aromatic rings. To illustrate their importance, of all the organic petrochemicals (hydrocarbons and their derivatives) produced industrially, over three-fourths are involved in the production of polymers. Some of the most important polymers are chlorinated hydrocarbons.