Ionization energy
The key idea
Ionization energy is the energy required to remove an electron from a gaseous atom or ion in a specified state. Successive ionization energies refer to successive electron removals.
Why it matters
Its periodic pattern is powerful but not perfectly smooth because subshell structure, pairing and shielding matter.
A picture to remember
Its periodic pattern is powerful but not perfectly smooth because subshell structure, pairing and shielding matter.