Here's why:

* Electronegativity: Fluorine is the most electronegative element, meaning it strongly attracts electrons.

* Valence Electrons: It has seven valence electrons in its outermost shell.

* Octet Rule: To achieve a stable configuration, it needs one more electron to complete its octet.

Therefore, fluorine forms one covalent bond with another atom to share one electron and complete its octet.