Successive ionization energies
The first ionization energy tells only part of the story. Removing a second, then a third electron can require much more energy, especially once removal reaches an inner shell.
Core idea
The first ionization energy tells only part of the story. Removing a second, then a third electron can require much more energy, especially once removal reaches an inner shell.
Example
For sodium, the first removed electron is the outer electron. The next energetic step is dramatically larger because removal now disturbs a much more stable inner configuration.
Common trap
A formula or trend is useful only when its definition and conditions of use are clear.
Check yourself
Explain the phenomenon in your own words, then identify which quantity or mechanism you would use to quantify it.
For sodium, the first removed electron is the outer electron. The next energetic step is dramatically larger because removal now disturbs a much more stable inner configuration.