Question

Electronegativity from boron to aluminium decreases and then increases marginally due to discrepancy in atomic raddi of elements what does it mean ( meaning of discrepancy in this context) ?

Answer 1

It is due to the screening effect ocuured in the d orbital of the elements so the 13th group elements have a slit change of behaviour
Boron behaves chemically like a nonmetal, whereas its heavier congeners exhibit metallic behavior. Many of the inconsistencies observed in the properties of the group 13 elements can be explained by the increase in Z_eff that arises from poor shielding of the nuclear charge by the filled (n − 1)d¹⁰ and (n − 2)f¹⁴ subshells. Instead of forming a metallic lattice with delocalized valence electrons, boron forms unique aggregates that contain multicenter bonds, including metal borides, in which boron is bonded to other boron atoms to form three-dimensional networks or clusters with regular geometric structures. All neutral compounds of the group 13 elements are electron deficient and behave like Lewis acids. The trivalent halides of the heavier elements form halogen-bridged dimers that contain electron-pair bonds, rather than the delocalized electron-deficient bonds characteristic of diborane. Their oxides dissolve in dilute acid, although the oxides of aluminum and gallium are amphoteric. None of the group 13 elements reacts directly with hydrogen, and the stability of the hydrides prepared by other routes decreases as we go down the group. In contrast to boron, the heavier group 13 elements form a large number of complexes in the +3 oxidation state.