What is the difference between the 3rd and 4th ionization energy values?

Question

Al and Ga are group 3A elements

Answer 1

Very high. Because the 3rd ionization energy is the amount of energy required to remove the third electron from one of these atoms - leaving a stable core. The 4th ionization energy involves removing the 4th electron which is in a fully occupied shell (i.e. it is a core electron).

Al

3rd I.E. 2745 kJ/mol

4th I.E. 11577 kJ/mol

Ga

3rd I.E. 2963 kJ/mol

4th I.E. 6180 kJ/mol

The Al3+ ion has a noble gas configuration (neon), whereas the Ga3+ ion has a 4d10 configuration. Because the Ga3+ ion doesn't have a noble gas configuration, it is easier to ionize than Al3+. However, the filled 4d subshell is quite stable, and, correspondingly, the 4th I.E. is over twice as high as the 3rd.