Here's why:

* Electronegativity: Fluorine is the most electronegative element, meaning it has a strong attraction for electrons.

* Octet Rule: Fluorine has 7 valence electrons. By gaining one electron, it achieves a stable octet configuration, fulfilling the octet rule.

* Ionization: To gain that extra electron, fluorine becomes negatively charged, forming the fluoride ion (F-).