It is not fluorine ion. It is fluoride ion. When a fluorine atom gains an electron it gains a negative charge. This is fluoride ion.
The covalent radius of fluorine is a measure of the size of a fluorine atom; it is approximated at about 60 picometres.
Since fluorine is a relatively small atom with a large electronegativity, its covalent radius is difficult to evaluate. The covalent radius is defined as half the bond lengths between two neutral atoms of the same kind connected with a single bond. By this definition, the covalent radius of F is 71 pm. However, the F-F bond in F2 is abnormally weak and long. Besides, almost all bonds to fluorine are highly polar because of its large electronegativity, so the use of a covalent radius to predict the length of such a bond is inadequate and the bond lengths calculated from these radii are almost always longer than the experimental values. Business Finance