Ionization Energy / Lewis Dot Structures

[Kathleen Vidanes 1E]

How do we know that Beryllium has a lower ionization energy than Chlorine when they are not within the same period or group?

[Carlos Gonzales 1H]

The trend in the periodic table is if you go from left to right, the ionization energy increases. Beryllium is on the left of the periodic table (alkali earth metals) and chlorine is on the right of the periodic table (halogens). Therefore, chlorine has higher ionization energy.

[AnuPanneerselvam1H]

Since the atomic radius decreases across a period, the energy required to remove an electron becomes higher. Therefore, ionization energy increases from left to right across a periodic table. Chlorine is to the right of beryllium and so it has a higher ionization energy.