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

1 Answer
anor277
Jul 2, 2016

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

Explanation:

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^-#

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