It seems to me that f-orbitals for lanthanide metals are treated as 'core-like' when a certain number of electrons have been removed.
Or, as Radiochemistry puts it,
The 4f binding energy is so great that the remaining 4f-electrons are regarded as "core-like". [Italic and emphasis added]
How is this justified exactly?
Effort
I am aware that
- each electron will be harder to remove as Culonic attraction increases with positive ionic charge,
and probably
- lathanide contraction is a part of the explanation.
You have to check out some of these other threads:
- Why don't we see these lanthanide species?
- What is meant by 'electrons of like/unlike rotation'?
- What's up with this quarter / three-quarter rule?
Original topic: Predominance of III oxidation state for lanthanides
