The Construcción principle: the improved Aufbau principle with 2 special filling rules

The Aufbau principle is used to predict electron configurations and to rationalise the block structure of the periodic table/spiral, yet it suffers from 2 main limitations, the inability to predict 20 “anomalous” configurations and reflect the true order of subshell energies, especially in the “d” and “f” block elements. This work introduces the Construcción principle, a unified framework that simultaneously accounts for both the ordering of differentiating electrons between successive elements and the energy of subshells, thereby predicting the observed electron configurations throughout the periodic table/spiral. This principle also incorporates relativistic stabilisation of s subshells in heavy elements. Moreover, 2 special filling rules are proposed to explain deviations from standard filling: (1) preferential occupation of larger and diffuse subshells by intraorbital repulsion at “d” and “f” block onsets, and (2) stabilisation of half-filled subshells through electron exchange. Prior to formulating these rules, the composition of Group 3 is critically examined using chemical and electronic evidence supporting the inclusion of lutetium and lawrencium in this group, thereby avoiding an artificial interruption of the “d” block against the filling rules. Accordingly, lanthanum and actinium should be regarded as the “anomalous” beginning of the “f” block, filling a d subshell instead of an f one in the formulation of Rule 1. Application of the Construcción principle, including its 2 special filling rules, reduces the number of “anomalous” configurations to only 2, palladium and thorium, yielding correct predictions of electron configurations and consequently, a clear periodic classification.