Why is fluorine highly electronegative?

Fluorine is the most electronegative element because of its unique combination of a small atomic size and its electronic structure.123

As a member of the halogen group, fluorine has seven valence electrons and requires only one more electron to achieve a stable, noble-gas electron configuration. Its small atomic radius allows the nucleus to exert a powerful attractive force on shared electrons in a covalent bond, effectively pulling them closer to itself than any other element.4123

This extreme ability to attract electrons is the defining characteristic of its electronegativity, which is the highest of all elements on the periodic table. Consequently, fluorine is the most reactive and powerfully oxidizing element, as it consistently seeks to acquire an additional electron to complete its valence shell.1324