How are electron affinity and ionization energy related?
One is the energy required to remove an electron from an atom. The other is the energy involved when an electron adds to an atom.
Ionization energy I is the amount of energy required to remove the outermost electron an atom. For example,
Ca → Ca⁺ + e⁻; I = 589.8 kJ/mol
Electron affinity EA is the amount of energy involved when an electron adds to an atom. For example,
Ca + e⁻ →Ca⁻; EA = 2.37 kJ/mol
In the Periodic Table, both the ionization energy and the electron affinity of an atom decrease as you go down a Group. They increase as you go across a period. But there are some exceptions to these patterns.