Why does fluorine react so violently?

Fluorine is exceptionally reactive because its atoms strongly want one more electron to complete their outer shell, and its tiny atomic size concentrates that pull. It has the highest electronegativity of any element, about 3.98 on the Pauling scale, so it tends to oxidize almost anything it contacts. Fluorine gas can attack glass, metals and water, which is why it must be handled with special materials. Chemists isolate it only with great care; it was first prepared in pure form in 1886 by Henri Moissan.