Zn which has the highest ionisation enthalpy in 3d series.The reason given in my textbook is:
The value of zinc is higher because it represent ionisation from 4s level.
This is not correct because for every 3d element ionisation is from 4s orbital. The explanation I found for this is from this site is:
Increase in nuclear charge outweigh the electron electron repulsion of 4s electrons rendering Zn an higher ionisation enthalpy than Cu.
This seems like a probable explanation but if Zn has higher ionisation enthalpy than Cu due to its increased nuclear charge.Why can't Zn have smaller atomic radius than Cu due to its increased nuclear charge which can decrease the size of the atom. But experimentally it has been found that Zn is bigger in size than Cu.
So why does Zn has the highest ionisation enthalpy in 3d series?
TEXT SOURCE:NCERT textbook (chapter:d and f block)