| Quantum Number | Symbol | Values | Meaning | |---|---|---|---| | Principal | ( n ) | 1, 2, 3... | Shell (energy level) & size | | Azimuthal (Angular) | ( l ) | 0 to ( n-1 ) | Subshell (shape): ( s ) (0), ( p ) (1), ( d ) (2), ( f ) (3) | | Magnetic | ( m_l ) | ( -l ) to ( +l ) | Orbital orientation | | Spin | ( m_s ) | ( +\frac12, -\frac12 ) | Electron spin (up/down) |