sentence2_structure: Aufbau principle<>gives<>the order of electron filling in an atom$$$the order of electron<>filling<>in an atom
sentence1: The relativistic stabilization of the 7s orbital is the explanation to the predicted electron configuration of darmstadtium, which, unusually for this group, conforms to that predicted by the Aufbau principle.
sentence2: Aufbau principle gives the order of electron filling in an atom.
question: What gives the order of electron filling in an atom?