Proper noun
the aufbau principle
(physics) The rule stating that, in the ground state of an atom or ion, electrons fill subshells of the lowest available energy, followed by subshells of higher energy.
Synonym: aufbau rule
This is due to the relativistic stabilization of the 7s 2 electron pair over the whole seventh period, so that none of the elements from 104 to 112 are expected to have electron configurations violating the Aufbau principle. Source: Internet