1.3.6—Determine the electronic configuration

Use this sequence for a ground-state configuration: (1) determine the species’ electron count, (2) fill sub-shells in increasing energy, (3) respect each sub-shell’s orbital capacity and Hund’s rule, and (4) add the superscripts to check the total. Use full or noble-gas shorthand notation as requested.

For an ion, start from the neutral atom’s proton number and adjust only the electron count for the charge. A positive ion has fewer electrons and a negative ion has more; the proton number and element identity do not change.

When forming a transition-metal ion, remove electrons from 4s before 3d, even though 4s was filled before 3d in the neutral atom. For example, Fe is [Ar] 4s² 3d⁶, whereas Fe²⁺ is [Ar] 3d⁶.

Reject a configuration if its superscripts do not match the species’ electron count or if it violates capacity, filling order or spin occupancy. Do not remove 3d before 4s or treat ion formation as a proton-number change; special Cr/Cu arrangements remain separate supported exceptions.