Explain ionization enthalpy and electronegativity for elements of the Boron family.

(N/A) Ionization Enthalpy: The ionization enthalpy values do not decrease smoothly down the group as expected from general trends. The decrease from $B$ to $Al$ is associated with an increase in atomic size.
The observed discontinuity in the ionization enthalpy values between $Al$ and $Ga$ and between $In$ and $Tl$ is due to the poor shielding effect of $d$- and $f$-electrons,which fail to compensate for the increase in nuclear charge. The order of ionization enthalpies is $\Delta_{i}H_{1} < \Delta_{i}H_{2} < \Delta_{i}H_{3}$.
Electronegativity: Down the group,electronegativity first decreases from $B$ to $Al$ and then increases marginally. This is due to the discrepancies in the atomic size of the elements.