This form of periodic table is congruent with the order in which electron shells are ideally filled according to the Madelung rule, as shown in the accompanying sequence in the left margin (read from top to bottom, left to right). The experimentally determined ground-state electron configurations of the elements differ from the configurations predicted by the Madelung rule in twenty instances, but the Madelung-predicted configurations are always at least close to the ground state. The last two elements shown, elements 119 and 120, have not yet been synthesized.
Column counts are columns only that contain elements. "Compact cells" denote cells with element symbol only, have navbox style and the table fits basic wiki page width (1024×768). "Detailed cells" have more data, and may cause page width excess (scroll bar added). "Extended" periodic tables are about theoretical periods 8 and higher (element 119 and higher).
