Fluorine
. 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 apa