fluorine (F) /flo͝or″ēn, flo̅o̅″ərēn/ [L, fluere, to flow] , an element of the halogen family and the most reactive of the nonmetals. Its atomic number is 9, and its atomic mass is 19.00. It occurs in nature only as a component of substances such as fluorspar, cryolite, and phosphate rocks. It can be prepared by the electrolytic decomposition of hydrogen fluoride and in its pure form is a pale yellow toxic gas 1.6 times heavier than air. It is also a component of very stable fluorocarbons used in the manufacture of resins and plastics. As a component of fluorides, it is widely distributed throughout the soils of the earth, enters plants, is ingested by humans, and is absorbed from the GI tract. Fluorides in the atmosphere and industrial dust are absorbed by the lungs and the skin. Relatively soluble compounds, such as sodium fluoride, are almost completely absorbed by humans. The relatively insoluble compounds, such as cryolite, are poorly absorbed. Small amounts of sodium fluoride are added to the water supply of many communities to harden tooth enamel and decrease dental caries. Excessive amounts of fluoride can mottle tooth enamel and cause osteosclerosis. Acute fluoride poisoning and death can result from the accidental ingestion of insecticides and rodenticides containing fluoride salts.
