QM describes the arrangement of electrons in the atom with 4 quantum numbers.
Principal quantum number: Localisation of electrons in shells
Azimuthal quantum number: Localisation of electrons in subshells of certain shaps
Magnetic quantum number: Spatial orientation of the subshells
Spin quantum number: exactly 2 electrons - of different spins - can be located in each subshell.
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TL;DR Axes vs. octant approach