Does this contradict the concept of electron shells in an atom, i.e. that the first shell can hold up to two electrons, the second up to eight, the third up to 18, etc.?
(I'm sure I don't understand all this. I've sat down and gone right through the chair onto the floor.)
No. But it is a fix, because THEOretically the electrons should be able to exist in random “spin” states but they don’t seem to when they are in the same atomic orbital. So that became the Pauli exclusion principle. It doesn’t explain “why” but it is a widely accepted lynchpin for further discovery.
Early “physics” was called “natural philosophy”...now it seems to be driven by mathematical philosophy coupled with experiments which affirm the math or cast doubt on the mathematical model. Every “understanding” nowadays of physics seem to be tentative because it can be based on different maths. When they discover “Maxwells Demons” that’s gonna be a hoot.
IMHO.
QED
No.
Each orbital can hold two electrons; one spin up, the other spin down.
The energy levels are denoted first by energy level, that’s the 1, 2, 3.
Then by subshell (orbital angular momentum), that’s the s, p, d, f,...
At the higher energy levela someimes the higher orbital angular momentum, are higher energy than the lowest angular momentum of the next shell. Those are the transition elements on the periodic table.
Go look up Aufbau process in a General Chem textbbok for details; the actual calculation of the energy levels involves quantum mrchanics, more specifically electron structure theory, and is beyond the scope of this comment.