A set of atoms, ions, or molecules are considered to share a similar electronic structure and the same number of electrons. These entities may exhibit vastly different chemical properties due to variations in nuclear charge, but their electron configurations are identical. For instance, the nitrogen anion (N3-), oxide anion (O2-), fluoride anion (F–), neon atom (Ne), sodium cation (Na+), magnesium cation (Mg2+), and aluminum cation (Al3+) all possess 10 electrons and a 1s22s22p6 electronic configuration.
Recognizing these relationships can be valuable in predicting and understanding trends in ionic radii, ionization energies, and other chemical behaviors. The concept provides a framework for simplifying complex chemical systems by focusing on the fundamental electronic arrangement, irrespective of the specific elements involved. Its historical development is rooted in the evolution of atomic theory and the understanding of electron configurations, contributing to the periodic trends observed in the elements.
