Here's why:

* Electronegativity: Fluorine is the most electronegative element on the periodic table. This means it has a strong attraction for electrons.

* Octet Rule: Fluorine has 7 valence electrons and needs one more to achieve a stable octet configuration.

* Gaining an Electron: To achieve stability, fluorine readily gains an electron, becoming a negatively charged ion called a fluoride ion (F-).