Why the first ionization energy for sodium is much smaller than the second ionization energy for sodium?

Answer 1

Ionization energy is referred to the amount of energy required to remove an electron from it's nucleus.

The first ionization energy refers to the valence electron (the electron on the outer most shell)

Blatantly, we can say that is requires less energy to remove valence electrons, rather than electrons in other orbitals, because it is farther away from the proton and therefore take less energy to remove that electron (ionization energy).

The large discrepancy between the first and second ionization energies can be accounted for, by some of these factors:

- such as shielding: basically the inner most electrons block some of the attractive forces from the nucleus (protons) and the valence electrons therefore have the most electrons blocking for them, because they are "in front" of all of the other electrons, on the outer most shell. Having this energy blocked means they are more free to move about.

-Inverse square relationship between the first and Nth (n) shell: I won't write the entire equation but basically:

the energy to be removed from the first shell is / by n^2, where n is the shell where the electron is removed from.

Hence for the first (n=1) shell

IE from 1st/ 1^2 = IE/1 = IE , this means that the energy to be removed from the first shell relative to itself is = which is true. This step is important.

However, if we use the second shell (n=2), this is the second ionization energy.

IE/2^2 = IE/4 , this means 4Xtimes LESS energy is needed to remove an electron from the second shell compared to the first

and then, if we use the third shell (n=3), which is the valence electron , also the FIRST Ionization energy.

IE/3^2 = IE/9 , this means 9Xtimes LESS energy is needed to remove an electron from the third shell compared to the first.

Conclusion: if we compare the first and second ionization energies, they are radically different from one another and there's a large discrepancy between the values due to the inverse square relationship between IE from the first energy level to the Nth level.

Answer 2

Because there is no such atom. Every second IE is greater than the first IE for the same element/isotope.