Georgia State University
Georgia State University: Hyper Physics: Ionization Energies
A concise description of ionization energy, and a line graph that plots the ionization energies of the first 88 elements vs. the atomic numbers.
Simon Fraser University
Chem1 Virtual Textbook: Periodic Trends in Ion Formation
Acting as a subtopic of the General Chemistry Virtual Textbook's section on Atoms and the Periodic Table, this site discusses electron affinity and ionization energy in relation to ion formation. Charts and graphs are included as well.