Question

How does `"electronegativity"` evolve with respect to the Periodic Table?

How do we rationalize this Periodic trend?

Answer 1

As we face the Periodic Table,.........electronegativity....

Explanation:

....electronegativity values INCREASE across the Period from LEFT to RIGHT, and DECREASE down a Group. This is something you should be able to remember.

How to rationalize this trend?

Electronegativity is defined as the ability of an atom involved in a chemical bond to polarize electron density towards itself. It makes sense that smaller elements towards the right of the Table, with higher nuclear charge, should attract their valence electrons. Of course, more electrons are added as we go across the Table, to go with the progressive increase in nuclear charge, but the INCOMPLETE valence electronic shell shields the `"nucular charge"` VERY imperfectly, and this also results in a contraction of the atomic radii.

And thus fluorine, oxygen, and nitrogen, are the most electronegative atoms on the Periodic Table.