1. Principle Q.#, n = 1, 2, 3, .... by integers, Shell(Level
Related to Average distance of e- from nucleus
 

2. Subsidiary Q.#, l= 0, 1, 2, ..., (n-1) by integers,  Subshell (Sublevel)
Related to shape of orbitals, each orbital of
the same shell and subshell has the same energy.
 

3. Magnetic Q.# , m_l = -, ..., 0, ..., integers, Orbitals
Related to orientation of orbital within subshell
 

4. Spin Q. #, m_s = +1/2, -1/2
Related to spin of e- about its own axis

max. # of e's per level = 2n²
max. # of e's /orbital = 2
# of subshells / shell = n
# of orbitals / subshell = 2 + 1

When an electron's subsidiary quantum # equals :

0  then the electron is in a "s" subshell
1  then the electron is in a "p" subshell
2  then the electron is in a "d" subshell
3  then the electron is in a "f" subshell
 

Hund's rule = Electrons occupy equivalent orbitals, unpaired to the maximum extent
possible, and with their spins parallel.

Pauli exclusion principle = No two electrons in the same atom can have the
same set of four quantum numbers; n, l , m_l, m_s.

Heisenberg's uncertainty principle = One can not determines simultaneously the
exact position and momentum (mass x velocity) of an object.