Question

How do electronegativity values change in groups and across periods?

Answer 1

An old mantra:

`"Electronegativity increases across a Period, and decreases"` `"down a Group"`

Explanation:

As you go from left to right n the Periodic Table on the same Period, atomic radii steadily decrease. Protons are being added to the nucleus as `Z` increases sequentially, and the nuclear charge increases. Of course, electrons are also being added to the valence shell, however, because they add to the same shell, they shield each other VERY IMPERFECTLY.

The result? Electronegativity increases. It is no coincidence that the most electronegative elements, `F`, and `O` occur to the right of the Periodic Table.

On the other hand, as you descend a Group, you are adding electrons to a new valence shell. The inner shell shields the nuclear charge. Also, the valence shell is farther removed from the nuclear charge. So down the Group, electronegativity decreases.

Remember the definition of electronegativity. Electronegativity is conceived to be the ability of an atom in a chemical bond to polarize electron density towards itself.