# Video: Identifying the Subshell Containing the Lowest-Energy Electrons for an Atom Containing Electrons in All Subshells in a Set

For a single atom with electrons in all of these subshells, which of the following is the subshell occupied by the lowest-energy electrons? [A] 2s [B] 3s [C] 3p [D] 4d [E] 4f

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### Video Transcript

For a single atom with electrons in all of these subshells, which of the following is the subshell occupied by the lowest-energy electrons? Electrons-filled subshells in order of increasing energy.

There are a number different rules for which subshells are higher in energy than others, which are summarized using this diagram. The question says that we have an atom with electrons in all of the subshells given in this answer choices. So, let’s create an electron configuration that would have all of these subshells, which we can do by following the arrows in this diagram.

According to our diagram, the 1s orbital comes first and two electrons can go in that subshell. The next is 2s, which can also have two electrons. The next would be 2p, which can have six electrons in that subshell in total, followed by 3s with our next two. 3p with the next six electrons, followed by 4s, then the 3d subshell, which can accommodate 10 electrons, followed by 4p and 5s. The 4d subshell would follow, then 5p, then 6s. And finally, our last answer choice is 4f, which when full, accommodates a total of 14 electrons.

The question asked us which subshells would be occupied by the lowest-energy electrons. And as we can see by filling our orbitals in order of increasing energy, the lowest energy subshell that’s one of our answer choices is 2s, which corresponds to answer choice (A).