Question Video: Identifying the Electronic Configuration of an Ion of Iron Chemistry

Video Transcript

Considering the electronic configuration of iron metal represented in the diagram, what is the electronic configuration of the Fe2+ ion?

This is a question about electronic configurations. The electronic configuration diagrams in this question show electrons as arrows pointing up or down. They show orbitals as squares filled with zero, one, or two electrons. And they show subshells as color-coded groups of orbitals: 3d in green and 4s in blue. The diagram to the right shows the electronic configuration of a neutral iron metal atom.

This question is asking which of these answer choices shows the electronic configuration of an iron two plus ion. It’s worth noting that each of these electronic configurations begins with the noble gas argon. This noble gas is a shortened way of showing the first 18 electrons of the iron metal atom. Argon’s 18 electrons completely fill the first three electron shells. The electrons represented by arrows in the diagram are the electrons that will partially fill the next electron shell.

Now that we know what the diagram signifies, we can attempt to answer the question. First, we should observe that there are six electrons in the 3d subshell and two more electrons in the 4s subshell. We should also note that when a neutral iron metal atom becomes an iron two plus ion, that involves losing two electrons to get that two plus charge. But which two electrons will it lose?

Well, atoms tend to lose the electrons with the highest energy levels, in other words the least stable electrons. In this case, that means the electrons in the 4s orbital. The four in 4s represents a higher energy level than the three in 3d. So the iron metal atom will give up the two electrons in the 4s orbital to form an iron two plus ion. As a result, the electronic configuration of our two plus ion will involve six electrons in the 3d subshell and zero electrons in the 4s subshell. This arrangement corresponds to the electronic configuration shown in answer choice (A), the correct answer.

Answer choice (A) differs from our initial diagram in that it is missing two electrons in the 4s subshell. These two electrons are the highest-energy electrons that the neutral atom gives up to become a two plus ion. So, what is the electronic configuration of the Fe2+ ion? That’s the electronic configuration depicted in answer choice (A).