Why Is Fluorine More Electonegative Than Chlorine, Bromine, and Iodine?

Fluorine is more electronegative than chlorine, bromine, and iodine because it has a smaller atomic size and a higher effective nuclear charge.

Electronegativity is the ability of an atom to attract electrons in a chemical bond. Fluorine is the most electronegative element due to its small atomic size and high effective nuclear charge. The effective nuclear charge refers to the net positive charge experienced by the outermost electrons. Fluorine has a high effective nuclear charge because it has a small atomic radius, meaning its electrons are closer to the nucleus and are more strongly attracted to it. This makes it more effective at attracting electrons compared to chlorine, bromine, and iodine.

As you move down the halogen group (from fluorine to iodine), the atomic size increases, and the effective nuclear charge decreases, which results in a lower electronegativity. The larger atomic radius means that the outer electrons are farther from the nucleus and experience less attraction. Hence, chlorine, bromine, and iodine are less electronegative than fluorine.