ABSTRACT
Elements in the periodic table are arranged in order of increasing atomic number, Z. The electrons of each element (equal in number to Z) fill the atomic orbitals in order of increasing energy, according to the rules of the Aufbau (or building-up) principle (see Topic G6). The locations in the periodic table which correspond to the sequential filling up of different types of orbital are shown in Fig. 1. The structure of the table reflects the recurrence of analogous electron
configurations; every element in a group (column) has the same configuration of valence electrons.
