The energy levels of one‑electron ions are given by the equation =(−2.18 aJ)22

where is atomic number, is the energy level, and aJ is the abbreviation for the unit attojoules.

Ionization energy is the energy needed to eject an electron from an atom or ion.

Calculate the ionization energy, , of the one‑electron ion Li2+. The electron starts in the lowest energy level, =1.