Now, according to my definition, ionization energy is the energy required to remove an electron from an atom. So to demonstrate that, we're going to use the following Beryllium atom. So Beryllium has 12344 Protons. So there are four protons within the nucleus, also four neutrons. And since our neutral atom has a charge of zero, that means if we have four protons, we must have four electrons. So two electrons are placed into the one s orbital, and two electrons are placed into the two s orbital.