Fluorine

Fluorine is the chemical element with symbol F and atomic number 9. It is the lightest halogen and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic molecules, F2. Fluorine is the most electronegative element. It is also the most reactive of all the elements, requiring great care in handling. The compounds of fluorine are called fluorides.
Symbol: F
Atomic number: 9
Electron configuration: [He] 2s2 2p5
Electronegativity: 3.98
Atomic mass: 18.998403 ± 0.0000005 u
Discoverers: Henri Moissan