Fluorine

[Sarah]

A non-metallic, gaseous element, strongly acid or negative, orassociated with chlorine, bromine, and iodine, in the halogen groupof which it is the first member. It always occurs combined, is veryactive chemically, and possesses such an avidity for most elements,and silicon especially, that it can neither be prepared nor kept inglass vessels. If set free it immediately attacks the containingmaterial, so that it was not isolated until 1886. It is a pungent,corrosive, colorless gas. Symbol F. Atomic weight 19.

[Sarah]

Fluorine is an extremely reactive and poisonous chemical element with atomic number 9.

[Sommer]

The chemical element of atomic number 9, a poisonous pale yellow gas of the halogen series. It is the most reactive of all the elements, causing very severe burns on contact with skin.