1.3.0—Scope note

Use this electron-structure sequence for ground-state atoms and ions within the assessed range hydrogen to krypton. The scope tells you which cases to handle; it is not a new chemical rule.

Within that range, describe electrons using principal shells, s/p/d/f sub-shells and orbitals, and use full or noble-gas shorthand configurations as required. Fill lower-energy sub-shells first, while keeping the stated 4s/3d ordering and any supported configuration exception in view.

For an ion, adjust the electron count for the charge and then write the configuration. For transition-metal ions, remove 4s electrons before 3d electrons; do not apply the neutral-atom filling order mechanically when forming the ion.

Do not import excited-state arrangements or examples beyond krypton into a scope-limited answer. Conversely, an out-of-scope example is not evidence that a broader chemical statement is false; it only lies outside the cases this card assesses. Ionisation-energy trends belong to the next Level-3 topic.