Question

Why electronegativity decreases from boron to aluminium and then increases in delhi?

Answer 1

$<u ><i>$ Answer :- Electronegativity of an element depends upon:

The size of the atom:- as the size decreases the electronegativity increases.
The magnitude of nuclear charge:- as the size decreases the attraction of the nucleus of the atom, towards the shared electron pair incraeses.
Electronegativity decreases from B to Al and then increases, This is due to the discrepancies of atomic sizes of the elements. On going from aluminium to gallium, the electrons start filling into the d-sub shells. Since, these intervening electrons do not screen the nuclear charge; hence the electrons in Ga experience more forces of attraction then in Al causing a decrease in atomic size and increase in electronegativity.

Hope this is clear to you!