How would you determine which of these elements has the highest first ionization energy?

1 Answer
Jul 2, 2016

How else but by experiment? But we can nevertheless determine the order.


Ionization energies INCREASE across the Period, going from left to right as we face the Table; but DECREASE down a Group.

We have the Noble Gases listed in their Periodic Order. The highest first ionization energy is undoubtedly that of #He#. Why? Because #He# is the smallest atom, and because helium has the greatest effective nuclear charge. Given what I have said, you should be able to determine the order of ionization energies:

#"Gas"+Deltararr"Gas"^+ + e^-#