sentence: Fluorine is the most reactive, while iodine is the least reactive.
sentences_before: The elements in the group are fluorine, chlorine, bromine, iodine, astatine, and ununseptium. They are very reactive, so they are likely to join with other elements on the left side of the periodic table to make compounds. This is due to the fact that they are missing one electron. They are rarely found alone in nature, except astatine, which is not found in nature.
sentences_after: Astatine is very radioactive and hard to get.
concept_name: fluorine
headings: Halogen
categories: Halogens