Which of the following is most likely to have the largest ratio of second ionization energy to first ...?

Question

ionization energy?
a.) stontium
b.) magnesium
c.) sodium
d.) potassium

Answer 1

You want an atom that is easy to take one electron from, but hard to take a second.

Removing an electron from Sr or Mg would give them a configuration isoelectronic with the alkali metals.
Which don't hold onto their electrons very well, and would have low ionisation energies.
So it's not a) or b).


Removing an electron from Na or K would give them a configuration isoelectronic with the noble gases.
Which would require a lot of energy to get the second electron from.

Hmm sodium or potassium ...

Sodium is a smaller atom than potassium, so it holds its valence electron tighter, and more energy is required to remove it.
But once it is isoelectronic with neon, it will have a much higher ionisation energy because it will be so much smaller.

Potassium's first ionisation energy is lower than sodium's, but the second ionisation value (when it is isoelectronic with argon)
will be lower than the sodium ion's, when it is isoelectronic with neon.

I'm going with sodium.

Answer 2

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