Ionization Energy - Ionization Energy of the Elements. It requires more energy to remove each successive electron. When all valence electrons have been removed, the ionization energy requires becomes more and more. It takes a lot of energy to remove core electrons.
▶ Atomic Radius, Ionization Energy, Electronegativity and Electron Affinity - YouTube
A brief periodic table trends activity for high school and genchem college students to learn about the 5 trends of the periodic table: ionization energy, electron affinity, metallic character, atomic radius, and electronegativity.