How would you account for the irregular of ionisation enthalpies (first) in the first series of the transition elements?

Explanation

Irregular variation of first ionization enthalpy . On moving from left to right along the first transiotn series,at effective nuclear charge increases, it is expected in general that the first ionization enthapy should show an increasing trend. However, the trend is irregular because removal of the electorn alters the relative energies of 4ss and 3d orbitals. thus, there is a reorganisation energy accompanying ionization. This results into the release of exchange energy which increases as the number of electrons increases in the `d^(n)` configuration and also from the transference of s-electrons ito d-orbitals. Cr has low first ionization energy because loss of one electron gives stable electronic configuratin `(3D^(5))` . Zn has very high ionization energy because electron has to be removed from 4s orbital of the stalbe configuration `( 3d^(10) 4s^(2))`.
Irregularities of second ionization enthalpy. After the loss of one electron, the removal of scond electron becomes difficult, Cr and Cu show much higher values because the second electron has to be removed from the stable configurations of `Cr^(+) ( 3d^(5))` and `Cu^(+) ( 3d^(10))`