Electron spin

2n square rule

https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Quantum_Mechanics/09._The_Hydrogen_Atom/Atomic_Theory/Electrons_in_Atoms/Electron_Spin

2,8,8,1

https://terpconnect.umd.edu/~wbreslyn/chemistry/electron-configurations/configurationPotassium.html