1.4.0—Scope note

Use ground-state electron configurations for the assessed ionisation-energy scope: atoms and ions are treated in their lowest-energy available arrangement, using the supported range from hydrogen to krypton.

Ionisation energy refers to removing one mole of electrons from one mole of gaseous species, one electron-removal step at a time, under the stated standard conditions. First ionisation uses gaseous atoms; successive ionisation uses the increasingly positive gaseous ions formed after earlier removals.

When successive-ionisation data are interpreted, use the ground-state configuration to locate the outer-shell electrons. A large jump means the next electron is being removed from an inner shell with stronger nuclear attraction; the number removed before that jump indicates the outer-shell count for the supported s- and p-block cases.

Do not use an excited-state promotion or an element outside the assessed range as the default configuration, and do not remove several electrons in one ionisation step. The scope limit defines the cases to apply; it does not claim that other states or elements cannot exist. Detailed trend explanations remain in the neighbouring ionisation-energy objectives.