How does electronegativity for the halogens?

Electronegativity is the ability of an atom in a chemical bond to polarize electron density towards itself. It makes sense that nuclear charge should increase gradually across the Period in the same valence shell, that is, in the same Period, with fluorine being the most electronegative element and the first member of Group VII. However, electronegativity decreases down the Group.

Electronegativitiy values decrease down a Group, a vertical column on the Periodic Table, because as one moves down the group, nuclear charge increases, but there is a full electronic shell between the nucleus and the valence electrons, with increased shielding effects. Consequently, nucleus/valence electron attraction should decrease.

Electronegativity increases as you move up and to the right across the halogens in the periodic table. Therefore, fluorine has the highest electronegativity among the halogens, followed by chlorine, bromine, iodine, and astatine.