How does shielding affect electronegativity?

I believe I'll illustrate with an example.

With a score of 4.0, fluorine (F) has the highest electronegativity of any element in the periodic table.

This is because all of its electron levels are drawn very close to the nucleus, resulting in very little shielding between the nucleus and the electrons, and its nucleus has a very strong attractive (effective nuclear charge) force directed towards all of its electrons.

In contrast, the element with the lowest electronegativity, francium, has a weight of 0.7.

Because francium is at the bottom of the first group, compared to fluorine, it has a lot more electron levels to hold onto, which results in more levels that shield the electrons from the positively charged nucleus.

Additional Information on Nuclear Charge Effectiveness!

Shielding reduces the effective nuclear charge felt by electrons, leading to decreased electronegativity.