Final answer:
To remove an electron from a positive ion requires more energy than from a neutral atom due to greater electrostatic attraction. This energy increases with the ion's charge because protons in the nucleus attract the fewer electrons left even more strongly. Successive ionization energies rise for each additional electron removed, especially when detaching core electrons.
Step-by-step explanation:
To remove an electron from a positive ion, you need more energy than removing one from a neutral atom. This is because a positive ion has a greater electrostatic attraction to the electrons remaining in the ion, as the number of protons in the nucleus outnumber the electrons. This attraction increases with the charge of the ion, meaning that a cation with a higher positive charge requires even more energy to remove an additional electron compared to an ion with a lower positive charge. For instance, Scandium (Sc) and Gallium (Ga) both have three valence electrons, and one can observe a sharp increase in ionization energy after the removal of these three electrons when moving to remove core electrons, which are more difficult to detach due to being closer to the nucleus and more tightly bound.
Ionization energy generally increases with each successive removal of an electron from an atom or ion because the electrons are held more tightly by the nucleus. Additionally, the energy needed to remove an electron becomes successively greater as you move deeper into the atom's electron shells. This trend is observable in successively charged ions, where each additional electron removed requires more energy than the previous one.