Fluorine, the lightest of the halogens, is the most rcactivc of all the elements, and it forms compounds with all the elements cxccpt the lighter inert gases. This great reactivity may be attributed to the large value of its electronegativity. Substanccs such as wood and rubber burst into flame when they arc held in a stream of fluorine, and even asbestos (a silicate of magnesium and aluminium) reacts vigorously with it and becomes incandcsccnt. Platinum is attacked only slowly by fluorine. Copper and steel can be used as containers for the gas; they are attacked by it, but become coated with a thin layer of copper fluoride or iron fluoride, which then protects them against further attack.
Bccausc its electronegativity is greater than that of any other clement, we cannot cxpect that fluorine could be prepared by reaction of any other element with a fluoride. It could have been made, however, by electrolysis of fluorides, sincc the oxidizing power (electron affinity) of an elcctrodc can be increased without limit by increasing the applied voltage. Fluorine was first obtained by the French chcmist Henri Moissan (1852-1907) in 1886 by the electrolysis of a solution of KF in liquid HF. The work must
have been extremely difficult, for it took him several years of hard experimenting to obtain free fluorine gas.
