Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Fluorine

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Fluorine (Latin fluo, “flow”), symbol F, chemically reactive, poisonous gaseous element. In group 17 (or VIIa) of the periodic table (see Periodic Law), fluorine is one of the halogens. The atomic number of fluorine is 9. The element was first isolated in 1886 by the French chemist Henri Moissan.

PROPERTIES AND OCCURRENCE

Fluorine is a pale, greenish-yellow gas, slightly heavier than air, poisonous, corrosive, and of penetrating and disagreeable odor. Its atomic weight is 18.998. Fluorine melts at -219.61° C (-363.30° F), boils at -188.13° C (-306.63° F), and has a specific gravity of 1.51 in its liquid state at its boiling point. It is the most chemically active of the nonmetallic elements. It combines directly with most elements and indirectly with nitrogen, chlorine, and oxygen. Nearly all compounds are decomposed by fluorine to form fluorides that are among the most stable of all chemical compounds.

Fluorine occurs naturally in the combined form as fluorite, cryolite, and apatite. Fluorite, from which most fluorine compounds are generally derived, is commonly mined in the United States from large deposits in northern Kentucky and southern Illinois. Fluorine also occurs as fluorides in seawater, rivers, and mineral springs, in the stems of certain grasses, and in the bones and teeth of animals. It is the 17th element in order of abundance in the crust of the earth.

USES

Fluorine compounds have many applications. The chlorofluorocarbons, odorless and nonpoisonous liquids or gases such as Freon, are used as a dispersing agent in aerosol sprays and as a refrigerant. In 1974, however, some scientists suggested that these chemicals reached the stratosphere and were destroying the earth's ozone layer. With confirmation of these findings by the late 1980s, the production of these chemicals began to be phased out (see Environment). Another chemical, Teflon, a fluorine plastic that is very resistant to most chemical action, is widely used to make such products as motor gaskets and dashboard accessories in the automobile industry. Teflon is also used as a coating on the inner surface of frying pans and other kitchen utensils to reduce the need for fat in cooking.

Fluorite or Fluorspar, mineral composed of calcium fluoride, the principal fluorine-bearing mineral. It occurs as cubic, isometric crystals and cleavable masses with a hardness of 4 and sp. gr. of 3-3.3. When pure, fluorite is colorless and transparent, or translucent with a glassy luster. It often occurs with impurities that make it yellow, blue, purple, green, rose, or brown. Several varieties exhibit fluorescence.

The mineral is usually found either in pure veins or associated with lead, silver, or zinc ores. It is common in limestone and dolomites and is occasionally found as an accessory mineral in pegmatites and other igneous rocks. Exceptionally clear crystalline fluorite is mined in Cumberland and Derbyshire, England.

Crystalline varieties, such as the fine-colored Derbyshire spar, are often carved into vases and other similar ornaments, and the variety chlorophane is used as a gem. The principal use of fluorite has been for the production of hydrofluoric acid, an essential raw material in the manufacture of synthetic cryolite and aluminum fluoride for the aluminum industry, and in many other applications in the chemical industry. Fluorite is also a standard flux used in the making of steel. Large quantities of fluorite are used in the production of enamel and opal glass, and perfect crystals are used for the manufacture of apochromatic lenses.