How does the size of the atom affects its electronegativity?

From top to bottom down a group, electronegativity decreases. This is because atomic number increases down a group, and thus there is an increased distance between the valence electrons and nucleus, or a greater atomic radius. Electronegativity is the ability for an atom of an element to attract the paired electron density in a bond to its' nucleus. Fluorine is the most electronegative element in the periodic table. A few factors affect it: ... Having a larger nucleus often means more electrons orbiting the nucleus.

Electronegativity is an atom's ability to attract additional electrones, forming positive and negative ions. As an atomic size increases, its electronegativity goes down.