(10) Which of the second period elements has the lowest second ionization energy?
Beryllium has the lowest second ionization energy. The relative sizes of ionization energies can be evaluated by the similarity of the electron configurations of the atoms to a noble gas electron configuration. The second period is the second row of the periodic table. Of these elements, beryllium is the only element that obtains a filled outer shell at the loss of a second valence electron. Its first ionization energy is not the least of the second period elements. However, once the first electron has been removed, removing the second electron is relatively favorable since it leaves an electron configuration equivalent to that of a helium atom.
