The toxic gas, fluorine, is the most reactive element. It was discovered by Karl Scheele in 1771 but not isolated until 1886 when Henri Moissan electrolysed potassium fluoride with some very sophisitcated and expensive equipment. The fluoride ion is detected in Chemistry and Society and its concentration in tap water is determined with precision in analytical chemistry using a selective ion electrode. K 84.95 Atomic radius A 0.57 Heat of vapor. The oxide is a strong acid.
Crystal are cubic.