Graph the general trends (left to right and top to bottom) in the second ionization energy (IE2) of an element as a function of its atomic number, over the range Z = 1-20. Label the minima and maxima on the graph with the appropriate element symbol.
Ionization energy is the amount of energy required to remove an electron from an atom's outermost orbital in its neutral ground state. As this hyperlink shows, the periodic trends for ionization energy are:
- It decreases as one moves down a group/ family. This is because as one moves down a group, more electron clouds (energy levels) are added. Thus, the negative electrons in the outermost orbital are further away from the positive nucleus and are shielded by more orbitals. This causes the valence electrons to be held on less tightly and easier to remove.
- Ionization energy increases as one moves from right to left. This is because as one moves across a period, the atomic radii decreases and the atom is smaller. Thus, the negative electrons are now closer to the positive nucleus and held on tighter. This causes such electrons to be more difficult to remove.
Second ionization energy is the amount of energy it takes to remove a second valence electron after a first has already been removed from the atom. Second ionization energies are greater than first ionization energies. However, they follow the same trends as above This is because there is a stronger positive pull from the nucleus for the electrons as the number of electrons decreases and the atom moves towards having a full outer orbital.
Therefore, atomic number 19 (potassium) would be the lowest second ionization energy on your graph. Helium, with an atomic number of 2, would have the greatest ionization energy.