There are 5 elements of the halogen family in column 17 of the Periodic Table. The word "halogen" comes from the Greek meaning "to produce sea salt," and all of them, with one exception, are very commonly found as compounds on Earth and within the oceans.
One of the properties of the Halogen family is that the elements are missing just one electron to complete their outer orbits. They are therefore reactive, and will share electrons among themselves. Again, with one exception, the whole family is diatomic, meaning that the element exists as a molecule made up of two of its atoms. The exception is astatine, which unlike its relatives, is among the rarest of elements.
The halogenic diatomic molecules are fluorine, chlorine, bromine, and iodine.
The 3 other remaining non-halogenic diatomic molecules are oxygen, hydrogen, and nitrogen.
Fluorine, Chlorine, Bromine, and Iodine