Now, my next question is where did this energy go? Well, this energy actually went into my atom system, into this atom. So that means that this cation has more energy than this neutral species, neutral Beryllium atom. So that means because this has a lower energy, this is more stable than this cation. So once again, ionization energy is the energy required to take away an electron from a neutral, in this case, a neutral atom. So on my periodic table, the ionization energies are labeled with the green numerical value.