Fluorine (F) has the smallest atomic radius among the given elements: fluorine, chlorine, bromine, iodine, and astatine.

As we move down a group (column) in the periodic table, the atomic radius generally increases. This is because new electron shells are added as we go down the group, and these new shells are further from the nucleus.

Therefore, fluorine, being at the top of the group of halogens, has the smallest atomic radius.