CHEM 121 glossary

Successive ionization energies

The energies to remove the first, second, third, … electrons one at a time ( $IE_1 < IE_2 < IE_3 < \dots$ ). They rise steadily, then jump sharply when a core electron must be removed; the number of electrons before the jump is the number of valence electrons.

Aluminium: the big jump comes after the third electron.

Example

Aluminium: 578, 1817, 2745, then 11 577 kJ/mol. The fourth electron comes from the $2p$ core, so Al has 3 valence electrons (group 13) and forms $\ce{Al^3+}$ .