Video Transcript
An atom of potassium has an electronic configuration of 1s2 2s2 2p6 3s2 3p6 4s1. How else can this electronic configuration be represented? (A) Open brackets Ar 4s1 close brackets. (B) Open brackets Ar close brackets 4s1. (C) Open brackets two Ne close brackets 4s1. (D) Open brackets Ne close brackets 4s1. Or (E) open brackets Kr close brackets 4s1.
An electronic configuration is the representation of the arrangement of electrons distributed among the orbitals and subshells. We can represent full electronic configurations as shown in the question for potassium by writing the subshells in order from lowest energy to highest energy and using superscript labels to show how many electrons there are in each subshell. The full electronic configuration of atoms can be quite long when we are dealing with elements that have high atomic numbers. It is sometimes easier to use bracketed noble gas notation, which is sometimes referred to as shorthand notation or an abbreviated electronic configuration.
Let’s illustrate how one can use the periodic table to generate the abbreviated electronic configuration for potassium. With the periodic table being organized in order of increasing atomic number, where atomic number is defined as the number of protons for that element, the neutral atoms of each element are, therefore, also organized in order of increasing number of electrons. As a result, the periodic table is essentially arranged based on the electronic configurations of the atoms of the elements.
To illustrate this, let’s begin by labeling the periods shown followed by the labeling of the s and p block. It should be noted that while this method works well for elements in the s and p blocks, it is not as effective for elements in the d and f blocks. Also notice the d block is not drawn to scale as the element this question is focused on is not found in the d block. In addition, since the element potassium is found in period four within the s block, we will not be worried about adding more details pertaining to the remainder of the periodic table.
The generic formula for writing shorthand notation for a neutral atom or ion firstly consists of splitting up the core electrons or inner electrons from the valence electrons or the electrons that reside in the highest energy levels. First off, potassium is found in period four and is in group one, which is labeled as s1. As for the other elements in the s and p blocks, an element’s position on the periodic table indicates the subshell that contains its valence electrons or electrons in the highest energy levels. That is why the full electronic configuration for potassium ends with 4s1, which means its valence electron resides in the 4s subshell. And the remaining 18 electrons are the core electrons that fill up each of the subshells that precede the 4s subshell or are lower in energy than the 4s subshell.
When it comes to writing electronic configuration in shorthand notation, the chemical symbol of the noble gas whose electronic configuration corresponds with the total core electrons for the element in question is written in brackets. In determining the correct noble gas, all of which reside in group 18, labeled p6 on this periodic table, first locate the chemical symbol for the element in question on the periodic table. The noble gas that is in the period above the period the element is in is the one that should be used in the brackets. The noble gas that is found in period three, the period above the period potassium is in, is argon, which means instead of writing out the location of the 18 core electrons in potassium as 1s2 2s2 2p6 3s2 3p6, which is argon’s electronic configuration, we can shorten it to the chemical symbol Ar in brackets followed by 4s1, the location of the valence electron for potassium. As a result, the correct answer is answer choice (B).
Let’s ensure this is the correct answer by taking a look at the remaining answer choices. When writing the bracketed noble gas portion of the shorthand notation, there should only be one chemical symbol or one noble gas indicated within the brackets. This eliminates answer choice (C), which has a coefficient number two in front of the neon chemical symbol. Another specific detail about shorthand notation is that only the chemical symbol of the noble gas should be in the brackets, while the subshell or subshells containing the outermost electrons should be written outside of the brackets. This eliminates answer choice (A), which has both the chemical symbol of the noble gas and the subshell with the valence electron inside of the brackets.
Looking at answer choices (D) and (E), they are both written in the proper shorthand format. However, if we were to write out the full electronic configuration for answer choices (D) and (E), we would find that, one, when adding up all the superscripts for each, they do not equal to the 19 electrons potassium contains and, two, they either skip subshells or repeat subshells, which is not correct.
Therefore, how else can the electronic configuration for potassium be represented? The answer is option (B) open bracket Ar close bracket 4s1.
