Fluorine

A non metallic gaseous element of atomic number 9 strongly acid or negative and associated with chlorine bromine and iodine in the halogen group of which it is the first member It always occurs combined is very active chemically and possesses such an avidity for most elements and silicon especially that it can neither be prepared nor kept in glass vessels but may be contained in lead vessels If set free it immediately attacks a containing glass vessel so that it was not isolated until 1886 It is a pungent corrosive colorless gas Symbol F Atomic weight 1900