Video Transcript
Put the following diagrams of
electronic configurations into the correct order to show the progression of an Mn
atom to an Mn2+ ion. (A) One, four, two; (B) three,
five, two; (C) two, five, three; (D) two, four, one.
In this question, we need to
identify which sequence of diagrams describes the formation of the Mn2+ cation. In other words, three of the five
numbered electronic configurations shown will occur in a specific order as the Mn
atom transitions to an Mn2+ ion. Let’s get started.
First of all, the atomic number of
manganese is 25. Therefore, a neutral manganese atom
has 25 positively charged protons and 25 negatively charged electrons. The electronic configuration of a
manganese atom is 1s2 2s2 2p6 3s2 3p6 4s2 3d5. The first 18 electrons of the
electronic configuration are the core electrons of the atom. These subshells can be condensed
using the symbol of the noble gas argon, because argon also contains 18
electrons. The electrons in the 4s and 3d
subshells are the valence electrons, which can be lost to form a cation.
In the provided diagrams, the blue
boxes represent the 4s subshell and the green boxes represent the 3d subshell. Let’s reverse the order of the 4s
and 3d subshells to reflect these diagrams. Now, it’s much easier to see this
electronic configuration matches diagram number two. In this diagram, there are exactly
five electrons in the 3d subshell and two electrons in the 4s subshell. Therefore, diagram two represents
the electronic configuration of a manganese atom before it becomes an ion.
In order to form an Mn2+ ion, the
manganese atom must lose two electrons. To write the electronic
configuration of the ion, electrons must be removed from the 4s subshell first
before the 3d subshell. This rule applies to all period
four transition metals. After removing one electron from
the 4s subshell, we see that the electronic configuration matches diagram four. Next, we need to remove a second
electron from the 4s subshell. The resulting electronic
configuration does not include a 4s subshell, because it is now empty. This result matches diagram number
one and is the electronic configuration of an Mn2+ ion.
In conclusion, the sequence of
diagrams that shows the progression of an Mn atom to an Mn2+ ion is two, four, one,
which corresponds to answer choice (D).
