Electronic Configuration of Atoms and Its Representation

The electronic configuration of an atom is simply the distribution of its electrons among its available orbitals in the ground state, built up by applying the Aufbau principle (energy order, Pauli's principle and Hund's rule together). There are two standard ways to WRITE it down. Orbital notation strings together each occupied subshell as $n s^{a} n p^{b} n d^{c}\ldots$, where the superscript gives the number of electrons in that subshell (for example, $1s^2\,2s^2\,2p^6$ for neon). Orbital-diagram notation instead draws a small box for every individual orbital in a subshell, with an up arrow (↑) or down arrow (↓) placed in a box to represent one electron of a particular spin; because it shows spins explicitly, the orbital-diagram form is the only one of the two that fully captures all four quantum numbers of every electron. For elements with a large atomic number, the plain orbital notation becomes a long string; this is shortened with a CONDENSED notation, which represents the electron configuration of the preceding noble gas — the 'core', identical for every element that follows it until the next noble gas — as that noble gas's symbol in square brackets, followed only by the 'outer' electrons specific to the element in question. Pot …