In representative elements the ionization energy values generally decrease smoothly down the group. But in boron group the values show an erratic trend. This is mainly due to :
inert pair effect in the heavier elements of the group
d-block contraction and lanthanide contraction affecting the values of later elements due to poor shielding by d and f electrons
the different type of packing in their crystalline structure
increase in metallic nature down the group

Question

In representative elements the ionization energy values generally decrease smoothly down the group. But in boron group the values show an erratic trend. This is mainly due to :
inert pair effect in the heavier elements of the group
d-block contraction and lanthanide contraction affecting the values of later elements due to poor shielding by d and f electrons
the different type of packing in their crystalline structure
increase in metallic nature down the group

Toppr Admin · Accepted Answer

Poor shielding of nuclear charge in Ga by 3d electrons results in smaller atomic size and higher I-P for the atom- Similarly- in TI the poor shielding by the 4f electrons leads to higher I-P or the atom- Hence- first I-P values for the 3rd group elements show erratic trend-

Poor shielding of nuclear charge in Ga by 3d electrons results in smaller atomic size and higher I.P for the atom. Similarly, in TI the poor shielding by the 4f electrons leads to higher I.P or the atom. Hence, first I.P values for the 3rd group elements show erratic trend.