Why's there a large jump in ionization energy between the second and third ionization energies for magnesium

Answer 1

The high school chemistry answer: The first two ionizations knocks out the 3s electrons, whereas the third needs to knock out a 2p electron. The screening effect of the inner shell electrons on the 3s electrons comes from everything in 1s, 2s, and 2p, but the screening effect on the 2p electrons 'only' comes from the 1s and 2s electrons (only is in quotes because this is not strictly true, but true enough that the effect is observed). So in effect, the 2p electrons see more charge (less shielding) than the 3s electrons, and thus require more energy to be removed.

Answer 2

Take a look at the electron configuration of Mg. [Ne]3s^2 or if you prefer 1s^2 2s^2 2p^6 3s^2 This tells you the number of electrons in the various energy levels. the first ionization energy is needed to remove the first electron from the 3s-orbital (the 3rd energy level) If you are not familiar with orbitals or enrgy levels think at them as "shells". Mg(g) ---> Mg^+ (g) + e^- The second ionization energy is needed to remove the 2nd electron from the 3s-orbital. Mg^+(g) ---> Mg^2+ (g) + e^- The 2nd energy is higher, because the nucleus has a positive charge +1 and this will increase the attraction forces between the nucleus and the electron. the 3rd ionization energy increases significantly as you have noticed. Why? because - the 3rd electron is in the 2s-orbital. It has a lower energy than the 3s-orbital, but it is closer to the nucleus, which has now a charge of +2. The attraction is therefore higher. - The "shielding" effect has been reduced. Between the 3rd electron and the nucleus are only the 1s^2 electrons. The noticable increase of 3rd. ionization energy is a typical pattern for a break in to lower energy levels!

Answer 3

The second ionization leads to the ion Mg++ which has an electronic configuration of Neon, 1s2 2s2 2p6 which is very stable.? When you ionise further, you obtain an electronic configuration less stable and so you need a huge of energy going from Mg++ to Mg+++ which is unstable and regains easily one electron