Hello. I have a question about ionization energy: Two hypothetical elements in the 2nd or 3rd period have the following ionization energies: Element X First: 800 kJ/mol Second: 2500 kJ/mol Third: 3900 kJ/mol Fourth: 23000 kJ/mol Element Y First: 700 kJ/mol Second: 2200 kJ/mol Third: 3500 kJ/mol Fourth: 19000 kJ/mol To what group in the periodic table should element X be in, and what charge should the ion in element X have? The answer is group 13 and charge +3. How could you possibly know this? I can see that the fourth energy level is far more than the third, so it should be somewhere between group 13-17, but how do you know which one?