Fluorine is an extremely toxic, pale yellow diatomic gas and the most chemically reactive element.
Core Principles & Analysis
Henri Moissan finally isolated fluorine by electrolysis in 1886 after decades of failed and sometimes fatal attempts by other chemists, earning the 1906 Nobel Prize.
It is the most electronegative and most reactive element, attacking nearly every material and even forming compounds with the noble gas xenon.
Fluorine appears in non-stick PTFE (Teflon), cavity-fighting fluoride toothpaste, and uranium hexafluoride, the gas used to enrich uranium for reactors.