Halogen

A family of five chemically-related, nonmetallic elements that includes bromine (Br²), fluorine (F²), chlorine (Cl²), iodine (I²), and astatine (At²). Halogens have a valence of one and readily form negative ions. They can combine with metals to form salts or replace hydrogen in many organic compounds. With the exception of astatine, the halogen family is widely used for a variety of sanitizing situations.

Source: GreenFacts

Fluoride