1.4.7—The electronic configurations of elements

Use successive-ionisation data to infer an atom’s outer-shell configuration: locate the largest jump, then count the electrons removed before that jump. Those electrons belonged to the outer shell; the next value begins removal from a new inner shell.

Combine the outer-electron count with the stated period or other supplied information. The period identifies the occupied principal shell, so the count can then be used to infer the relevant outer sub-shells and write the supported ground-state configuration.

For example, a first large jump after seven removals supports seven outer electrons; with Period 3 information, the outer arrangement is 3s²3p⁵. Treat this as evidence-led deduction from the jump and the supplied period, not as a guess from the jump alone.

A jump gives the number of outer electrons, not automatically the element. Check the period, the gaseous-ion sequence and the supported configuration scope before naming an element; do not confuse a shell jump with the smaller within-shell or sub-shell changes.