What is the electronegativity trend for elements in the same chemical group that form anions?
AS we look at the Table
As we face the Table,
Two factors are important here: (i) nuclear charge; and (ii) shielding by other electrons.
Across the Period, nuclear charge increases sequentially, and the incomplete electronic shell shields the nuclear charge very imperfectly. And thus as we go across the Period from left to right as face the Table, electronegativity sequentially increases, to reach a maximum at fluorine, which is the most electronegative element. This trend is also observed in the marked decrease in atomic radius across the Period in the same direction.
Down the Group, the nuclear charge is shielded somewhat by complete electronic shells. Of course, as
On the Pauling scale, which used actual ionization enthalpies, and electron affinities, fluorine at
Electronegativities thus follow a pronounced Periodic trend.