## Chemistry: The Molecular Science (5th Edition)

First ionization energy: $1s^22s^22p^63s^23p^6$ Second ionization energy: $1s^22s^22p^63s^23p^5$ After the first ionization, potassium is in a stable noble gas configuration. Thus, removing the second electron is much harder as it requires more energy to remove electrons when the ion is stable.