Explain ionization enthalpy and electro-negativity for elements of Boron family.

Ionization enthalpy : The ionisation enthalpy values as expected from the general trends do not decrease smoothly down the group. The decrease from $B$ to $Al$ is associated with increased in size.

The observed discontinuity in the ionisation enthalpy values between $\mathrm{Al}$ and $Ga$ and between In and $\mathrm{Tl}$ are due to inability of $d$ - and $f$-electrons, which have low screening effect, to compensate the increase in nuclear charge. The order of ionisation enthalpies, as expected, is $\Delta_{i} \mathrm{H}_{1}<\Delta_{i} \mathrm{H}_{2}<\Delta_{i} \mathrm{H}_{3} .$

Electronegativity : Down the group, electro-negativity first decreases from $B$ to $Al$ and then increases marginally. This is because of the discrepancies in atomic size of the elements.