ionization energy A level chemistry AQAWatch this thread
The second ionization energy of calcium is lower than the second ionization of potassium because the second electron calcium has to be removed from s orbital which has a slightly lower energy than the potassium electron which has to be removed from the d orbital. Secondly the ionization energy is lower than the potassium because d orbital is shielding the electron in the s orbital therefore even though the nuclear charge increased the atomic radi and the shielding outweigh the nuclear charge.
would this give me full marks.
K doesn't use its d subshell.
And anyway, after you remove 1 e- from K, it will be 2.8.8 and the 2nd e- is therefore coming from the 3rd shell, whereas Ca still has 22.214.171.124 and its 2nd e- is coming from a much higher 4th shell.