Video: Identifying the Element with the Highest Second Ionization in a Set of Elements on an Abbreviated Periodic Table

Which of the letters corresponds to the element with the highest second ionization energy?

03:57

Video Transcript

Which of the letters corresponds to the element with the highest second ionization energy?

We’re given an abbreviated periodic table with most of the elements missing and some of them filled in. The second ionization energy is the energy that’s needed to remove an outer electron from a plus one ion. So, this would be the energy you need to remove an electron from a plus one ion so that you end up with a plus two ion. Remember that electrons are attracted to the nucleus of an atom, so removing an outer electron means that we need to put in energy to overcome this attraction to the nucleus.

Successive ionization energies, so the second ionization energy or higher, is always going to be larger than the first ionization energy. This is because in the second ionization energies and higher ionization energies, we’re removing an electron from a species that’s positively charged, which means that there’s more protons than there are electrons. Since there’s more protons than electrons, the outer electrons are being attracted to the nucleus more than they would be in a neutral atom.

Higher ionization energies follow the same general trend as the first ionization energy. And that it decreases going down a group and increases across a period moving left to right. But there are some interesting exceptions in the second and higher ionization energies. Let’s look at the first three ionization energies for both lithium and beryllium, which are right next to each other on the periodic table. This question is about the second ionization energy, not the third. But looking at all three will give us a good idea of the trend that’s occurring here.

Looking at the first three ionization energies for lithium, we’ll see that between the first two ionization energies, there’s an enormous jump. This is a factor of 14 increase between the two. Between the second and the third, there is an increase, but it’s not as dramatic as between the first and the second. Between the second and the third, the ionization energy only increases by about a factor of two.

If we look at the first three ionization energies of beryllium, there’s an enormous jump between the second and the third ionization energies. The second ionization energy of beryllium is actually lower than the second ionization energy of lithium. So, what’s going on here?

Well, lithium has just one outer electron and beryllium has two. So, for the first ionization energy we remove lithium’s one outer electron. And the remaining ionization energies are removing the core electrons from lithium. So, the second ionization energy for lithium is so much higher than the first because we’re removing a core electron, not an outer electron.

Beryllium has two outer electrons. So, there’s two electrons that we can remove before we start removing core electrons. This is reflected by the large jump in the third ionization energy that we see in beryllium just like we see in lithium. Lithium just has fewer outer electrons, so this jump happened sooner.

In this question, we want to identify which element will have the highest second ionization energy. So, the answer to this question will probably be similar to what we see in lithium, where the second ionization energy is really high because we’re removing a core electron. However, lithium isn’t an answer choice. So, the element that we’re looking for must be A because, like with lithium, A only has one outer electron. So, its second ionization energy will be really high because we’re trying to remove a core electron.

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