Fluorine

Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. As the most electronegative element, it is extremely reactive, as it reacts with almost all other elements, except for helium and neon.

Characteristics:

Group17 Melting point−219.67°C, −363.41°F, 53.48 K 
Period2 Boiling point−188.11°C, −306.6°F, 85.04 K 
Blockp Density (g cm−3)0.001553 
Atomic number9 Relative atomic mass18.998  
State at 20°CGas Key isotopes19F 
Electron configuration[He] 2s22p5 CAS number7782-41-4