Question

The difference between the third and fourth ionization energies of scandium is much larger than the difference between the third and fourth ionization energies of titanium. why?

Answer 1

This is because removing three electrons means third ionization energy would leave scandium with a full valence shell that is 3s²3p⁶ and removing a fourth electron would begin to remove electrons from a full valence shell which is very energetically not favorable.

Removing a third and fourth electron from titanium is bringing Ti closer and closer to having an empty 4th energy level and a completely full 3rd energy level. Removing the 4th electron would be very energetically favorable because it would result in a full valence shell.