This chart compares first ionization energy (energy to remove an electron) with electron affinity (energy released when gaining an electron) for each element.

The inverse relationship is revealing: elements that strongly attract electrons (high electron affinity) are also hard to ionize. Halogens top the electron affinity chart as they need just one electron to complete their shell. Alkali metals have low ionization energies, easily losing their single valence electron. This explains ionic bond formation between metals and nonmetals.