Ionization Energy & Electron Affinity

Generally the (n+1)th ionization energy is larger than the nth
ionization energy. Always, the next ionization energy involves removing
an electron from an orbital closer to the nucleus. Electrons in the
closer orbitals experience greater forces of electrostatic attraction;
thus, their removal requires increasingly more energy.
Large jumps in the successive molar ionization energies occur when
passing noble gas configurations. For example, as can be seen in the
table above, the first two molar ionization energies of magnesium
(stripping the two 3s electrons from a magnesium atom) are much smaller
than the third, which requires stripping off a 2p electron from the very
stable neon configuration of Mg²⁺.


Periodic trend for ionization energy. Each period begins at a minimum
for the alkali metals, and ends at a maximum for the noble gases.





Ionization energy is also a periodic trend within the periodic table organization. Moving left to right within a period or upward within a group, the ionization energy
generally increases. As the atomic
radius decreases, it becomes harder to remove an electron that is
closer to a more positively charged nucleus.

Background Reading for Ionization Energy & Electron Affinity