Compare and contrast the second ionization energies of K and Ca?

Nov 29, 2017

The energies can be easily looked up. The question is, "What makes them so different?" The answer is in the stability of the resulting electron shell.

Explanation:

The "second ionization" means that the first valence electron has already been removed. For Ca this means that it's valence shell is still "imbalanced" - it really wants to lose another electron to get to a more stable electronic configuration ($C {a}^{2 +}$).

On the other hand, K has reached a stable configuration after the first electron loss (${K}^{1 +}$). Removing the next one requires overcoming not only the charge/attraction difference of the protons to the remaining electrons - as it does with Ca as well - but creating a less stable electronic configuration for the atom.

Ca second ionization energy: $1145.4 k \frac{J}{\text{mol}}$
K second ionization energy: $3052 k \frac{J}{\text{mol}}$