What is the electron configuration of Co²⁺ and how many unpaired electrons are in the free transition metal ion?

(a) [Ar]3d⁵4s²; 5 unpaired electrons

(b) [Ar]3d⁵4s²; 1 unpaired electron

(c) [Ar]3d⁷; 3 unpaired electrons

(d) [Ar]3d⁷; 1 unpaired electron

Video transcript

All right. Hi, everyone. So for this question, let's provide the electron configuration of the free N I two positive ion and determine the number of unpaired electrons. So here we have four different answer choices. Each proposing a different electronic configuration for the ion in question and also either two or four unpaired electrons. So the most efficient route is to find the electronic configuration of the neutral nickel atom. And recall that when an atom is neutral, the number of electrons is equal to the number of protons. So because nickel has an atomic number of 28 according to the periodic table, nickel is going to have 28 electrons when it is neutral, right? Because the atomic number is equal to the number of protons. Now, the innermost electrons can be represented by the noble gas immediately before the element in question, which in the case of nickel happens to be argon, that would account for 18 of the 28 electrons. This means that the remaining 10 electrons should be distributed among the four S and 3d orbitals. Now recall that s orbitals can hold a maximum of two electrons whereas D orbitals can hold a maximum of 10. So after the argon noble gas corp are two electrons in the four s orbital followed by the remaining eight in the 3d orbital, giving us an electronic configuration of argon for us 238 or a neutral nickel atom. Now recall that to achieve a positive charge electrons have to be removed from the highest energy levels. So in the case of nickel here, that has a charge of positive 22 electrons must be removed from the highest energy level, which in this case is the four s orbital. So in this case, both electrons from the four s orbital are removed to leave an electronic configuration of Argon 3d 8. So now to find the total number of unpaired electrons, we have to consider the distribution of these electrons in the 3d orbital. Now here recall that the 3d orbital has five lines right or five sub units. So to speak, each of which can hold a maximum of two electrons. So in this case, all of the 3d orbitals are filled according to both the abau principle and H's rule, the elf B principle states that the lowest energy orbitals are completely filled. First in Hans rule states said orbitals of the same energy level have to be half filled before they are paired. So in this case, according to hand rule, all of these same energy orbitals must be half filled, which means that all five of them receive one unpaired electron first and then the remaining three electrons are placed in these orbitals to create pairs. This means that three of the orbitals here are fully filled, whereas two of them contain unpaired electrons, meaning that our eye on here has an electronic configuration of Argon 3d 8 and has two un paired and electron. Meaning that our answer here is going to be option c in the multiple choice and there you have it. So with that being said, thank you so very much for watching. And I hope you found this helpful.