How is Aufbau principle derived or proved?
on a note, why does the energy of 3d subshell is More than that of 4s subshell, instead
as 4s is greater in extent than 3d,4s should have greater energy!
though I have read the answers here
Could the Periodic Table have been done using group theory?
Aufbau principle in modern quantum theory
I cannot find a definite explaination or proof of the above theory(rule)
