List three halogens, and describe a property

that they all share.

The halogen group are fluorine, chlorine, bromine, iodine, and astatine. The halogenic elements all have seven valence electrons; they only require one electron to fill their outer shells, giving them an oxidation number of - 1. Also, the halogens form diatomic molecules (e. g., Cl₂) in their elemental states.

Additionally, the halogens act like oxidizing agents, exhibiting the ability to oxidize metals. In fact, the name halogen is derived from the Greek meaning "salt former", referencing the fact that the halogens form salts when they react with metals.