Chemistry and Chemical Reactivity (9th Edition)

K: group 1, period 4 $[Ne]\ 3s^2\ 3p^6\ 4s^1$ $K^+: [Ne]\ 3s^2\ 3p^6$ $K^{2+}: [Ne]\ 3s^2\ 3p^5$ In the second ionization energy, an electron would have to be removed from an inner shell and break a noble gas electronic configuration.