Periodic trends in first ionization energy and electron affinity across rows and down columns of the periodic table arise from the interplay between nuclear charge (Z), electron shielding, and effective nuclear charge (Z_effective), which determine how tightly an electron is bound to an atom. Ionization energy is the energy required to remove the highest-energy (least tightly bound) electron and is always positive; electron affinity is the (possibly negative) energy change upon adding an electron to a neutral atom or ion, reflecting the resulting species' relative stability. These trends, along with photoelectron spectroscopy as an experimental method for measuring orbital binding energies, belong to atomic structure and periodicity within general/physical chemistry, connecting quantum-mechanical orbital energy ordering to macroscopic periodic table organization.
Periodic trends in first ionization energy and electron affinity across rows and down columns of the periodic table arise from the interplay between nuclear charge (Z), electron shielding, and effect…