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Science EncyclopediaScience & Philosophy: Categorical judgement to Chimaera

Chemistry is the science that studies why materials have their characteristic properties, how these particular qualities relate to their simplest structure, and how these properties can be modified or changed. The term chemistry is derived from the word alchemist, which finds its roots in the Arabic name for Egypt al-Kimia. The Egyptians are credited with being the first to study chemistry. They developed an understanding of the materials around them and became very skillful at making different types of metals, manufacturing colored glass, dying cloth, and extracting oils from plants. Today, chemistry is divided into four traditional areas: organic, inorganic, analytical, and physical. Each discipline investigates a different aspect of the properties and reactions of the substances in our universe. The different areas of chemistry have the common goal of understanding and manipulating matter.

Organic chemistry is the study of the chemistry of materials and compounds that contain carbon atoms. Carbon atoms are one of the few elements that bond to each other. This allows vast variation in the length of carbon atom chains and an immense number of different combinations of carbon atoms, which form the basic structural framework for millions of molecules.

The word organic is used because most natural compounds contain carbon atoms and are isolated from either plants or animals. Rubber, vitamins, cloth, and paper represent organic materials we come in contact with on a daily basis. Organic chemistry explores how to change and connect compounds based on carbon atoms in order to synthesize new substances with new properties. Organic chemistry is the backbone in the development and manufacture of many products produced commercially, such as drugs, food preservatives, perfumes, food flavorings, dyes, etc. For example, scientists recently discovered that chlorofluorocarbon containing compounds, or CFCs, are depleting the ozone layer around the earth. One of these CFCs is used in refrigerators to keep food cold. Organic chemistry was used to make new carbon atom containing compounds that offer the same physical capabilities as the chlorofluorocarbons in maintaining a cold environment, but do not deplete the ozone layer. These compounds are called hydrofluorocarbons or HFCs and are not as destructive to the earth's protective layer.

Inorganic chemistry studies the chemistry of all the elements in the periodic table and their compounds, except for carbon-hydrogen compounds. Inorganic chemistry is a very diverse field because it investigates the properties of many different elements. Some materials are solids and must be heated to extremely high temperatures to react with other substances. For example, the powder responsible for the light and color of fluorescent light bulbs is manufactured by heating a mixture of various solids to very high temperatures in a poisonous atmosphere. An inorganic compound may alternatively be very unreactive and require special techniques to change its chemical composition. Electronic components such as transistors, diodes, computer chips, and various metal compounds are all constructed using inorganic chemistry. In order to make a new gas for refrigerators that does not deplete the ozone layer, inorganic chemistry was used to make a metal catalyst that facilitated the large scale production of HFCs for use throughout the world.

Physical chemistry is the branch of chemistry that investigates the physical properties of materials and relates these properties to the structure of the substance. Physical chemistry studies both organic and inorganic compounds and measures such variables as the temperature needed to liquefy a solid, the energy of the light absorbed by a substance, and the heat required to accomplish a chemical transformation. Computers may be used to calculate the properties of a material and compare these assumptions to laboratory measurements. Physical chemistry is responsible for the theories and understanding of the physical phenomenon utilized in organic and inorganic chemistry. In the development of the new refrigerator gas, physical chemistry was used to measure the physical properties of the new compounds and determine which one would best serve its purpose.

Analytical chemistry is the area of chemistry that develops methods to identify substances by analyzing and quantifying the exact composition of a mixture. A material may be identified by measurement of its physical properties. Examples of physical properties include the boiling point (the temperature at which the physical change of state from a liquid to a gas occurs) and the refractive index (the angle at which light is bent as it shines though a sample). Materials may also be identified by their reactivity with various known substances. These characteristics that distinguish one compound from another are also used to separate a mixture of materials into their component parts. If a liquid contains two materials with different boiling points, then the liquid can be separated into its components by heating the mixture until one of the materials boils out and the other remains. By measuring the amount of the remaining liquid, the component parts of the original mixture can be calculated. Analytical chemistry can be used to develop instruments and chemical methods to characterize, separate, and measure materials. In the development of HFCs for refrigerators, analytical chemistry was used to determine the structure and purity of the new compounds tested.

Chemists are scientists who work in the university, the government, or the industrial laboratories investigating the properties and reactions of materials. These people research new theories and chemical reactions as well as synthesize or manufacture drugs, plastics, and chemicals. Today's chemists also explore the boundaries of chemistry and its connection with the other sciences, such as biology, physics, geology, environmental science, and mathematics.

Applications of new theories and reactions are important in the field of chemical technology. Many of the newest developments are on the atomic and molecular level. One example is the development of "smart molecules" such as a polymer chain that could replace a fiber optic cable. The chemist of today may have many socalled non-traditional occupations such as a pharmaceutical salesperson, a technical writer, a science librarian, an investment broker, or a patent lawyer, since discoveries by a traditional chemist may expand and diversify into a variety of fields which encompass our whole society.

Further Reading

Castellan, G.W. Physical Chemistry. Addison-Wesley, 1983.

Hargis, L. Analytical Chemistry: Principles & Techniques. Prentice-Hall, 1988.

Huheey, J. Inorganic Chemistry. New York: Harper & Row, 1983.

McMurry, J. Organic Chemistry. Pacific Grove, CA: Brooks/Cole Publishing Co., 1992.

Segal, B. Chemistry, Experiment and Theory. New York: John Wiley & Sons, 1989.


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Analytical chemistry

—That area of chemistry that develops ways to identify substances and to separate and measure the components in a mixture.

Inorganic chemistry

—The study of the chemistry of all the elements in the periodic table and their compounds except for carbon-hydrogen compounds.

Organic chemistry

—The study of the chemistry of materials and compounds that contain carbon atoms.

Physical chemistry

—The branch of chemistry that investigates the properties of materials and relates these properties to the structure of the substance.

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