Why do electrons farther from an atomic nucleus come off more easily?

Electrons farther from an atomic nucleus are removed more easily because they experience a weaker electrostatic attraction to the nucleus.1

In an atom, all electrons are held by the positive charge of the nucleus. The energy required to remove an electron—known as ionization energy—is a measure of how strongly an electron is bound to the atom. Because the attractive force between the nucleus and an electron decreases as the distance between them increases, valence electrons in larger atoms are held less firmly than those in smaller atoms. Consequently, these outer electrons require less energy to be removed, making them more readily available for chemical reactions and bond formation.12

Conversely, electrons closer to the nucleus, such as those in inner shells, are gripped much more strongly by the positive nuclear charge, resulting in significantly higher ionization energies.1