Here's why:

* Fluorine's Electron Configuration: Fluorine has 9 electrons, with the electronic configuration 2, 7. This means it has 7 electrons in its outermost shell (valence shell).

* The Octet Rule: Atoms tend to gain, lose, or share electrons to achieve a stable configuration with 8 electrons in their outermost shell (the octet rule).

* Gaining an Electron: For Fluorine to achieve an octet, it's easier for it to gain one electron. This results in a full outer shell with 8 electrons and a net charge of -1.

Therefore, a Fluorine ion is typically represented as F⁻.