Basically the Pauli exclusion principle allows only 1
Fermion for each available energy level (spin 1/2 particle such as electrons - spin 1 particles such as protons are called Bosons and do not have this restriction).
The Bohr theory also called the Bohr-Sommerfeld theory only goes as far
as describing the allowed values of the orbital angular momentum of the electron.
However, the electron has additional properties, namely its spin angular
momentum and its magnetic moment. So within the allowed values for
"Bohr" angular momentum a splitting of the available energy states
occurs when these additional properties of the electron are considered,
but there will still be no more than 1 electron occupying each energy
state under the Pauli exclusion principle.
Hope this simplified explanation helps!
I understand this but how does Pauli's exclusion principle help explain fine structures. Because i was asked this but i don't think that pauli's exclusion principle is required to explain fine structures.
Well you have energy levels that split into what is knwn as the fine structure and you have the pauli exclusion principle that states that no two fermions may exist in the same quantum state. Why do you think electrons split into different energy levels?
I think that the Pauli Principle is generally credited with explaining the
structure of the atoms in the periodic table (and thus the associated
energy levels) more than it is in explaining the fine spectral lines.
However, the fine spectral lines confirm the atomic structure as
postulated in the exclusion principle.
Consider the structure of atoms not constrained by the exclusion principle - all of the electrons in a ground state atom would be clustered
around the nucleus in a single (the lowest) energy state. That would
seem to complicate things considerably - there wouldn't even be
valence electrons to explain chemical reactions