---

Example 6.13: Ranking Ionization Energies

Predict the order of increasing energy for the following processes: \(E_{\mathrm{I1}}\) for Al, \(E_{\mathrm{I1}}\) for Tl, \(E_{\mathrm{I2}}\) for Na, \(E_{\mathrm{I3}}\) for Al.

Solution

Removing the 6p^1 electron from Tl is easier than removing the 3p^1 electron from Al because the higher n orbital is farther from the nucleus, so \(\ce{IE1(Tl)}\) < IE1(Al). Ionizing the third electron from Al(Al^2+ ->\(\ce{ Al^3+}\) +e-) requires more energy because the cation \(\ce{Al^2+}\) exerts a stronger pull on the electron than the neutral Al atom, so \(\ce{IE1(Al)}\) < IE3(Al). The second ionization energy for sodium removes a core electron, which is a much higher energy process than removing valence electrons. Putting this all together, we obtain: IE1(Tl) < IE1(Al) < IE3(Al) < IE2(Na).