What does this mean.....(line taken fron NCERT)
the irregular trend in the first ionisation enthalpy of the 3d metals can be accounted for by considering that the removal of one electron alters the relative energies of 4s and 3d orbitals. so the unipositive ions have dn configurations with no 4s electron. there is thus, a reorganisation energy accompanying ionisation with some gains in exchange energy as the no. of electrons increases and from the transference of s into d orbitals...

Dear Student

4s has 2 electrons, but 3d has 10.
If we remove electrons from 4s, it is much easier than removing from 3d.
So, the anomaly is observed when usually, +1 charge is the case. The I.E. of 4s being much less, it is easily removed.
In some cases like Cu(I), you can clearly see that is is 3d10 4s1 for Cu element. but for Cu(I) is 3d10.

Regards

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