ELECTRONIC KERNEL CONFIGURATION: CONSTRUCTION, EXAMPLES - CHEMISTRY - 2025

The compact or kernel electron configuration is one whose quantum notations for the number of electrons and their energy sublevels are abbreviated by the noble gas symbols in brackets. It is very useful when writing electronic configurations for a certain element, as it is simple and fast.

The word 'kernel' usually refers to the inner electronic shells of an atom; that is to say, those in which their electrons are not of valence and therefore do not participate in the chemical bond, although they do define the properties of the element. Metaphorically speaking, the kernel would be the interior of the onion, with its layers composed of a series of orbitals increasing in energy.

Electronic configurations abbreviated with the noble gas symbols. Source: Gabriel Bolívar.

The image above shows the chemical symbols for four of the noble gases in brackets and in different colors: (green), (red), (purple), and (blue).

Each of its dotted frames contains boxes that represent the orbitals. The larger they are, the greater the number of electrons they contain; which in turn will mean that the electronic configurations of more elements can be simplified with these symbols. This saves time and energy writing all the notations.

Build order

Before using kernel electron configurations, it is a good idea to review the correct order to build or write such configurations. This is governed according to the rule of diagonals or Moeller diagram (called in some parts the rain method). Having this diagram at hand, the quantum notations are as follows:

1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p

This string of quantum notations looks strenuous; and it would be even more so if it had to be written every time the electron configuration of any element found in period 5 onwards was going to be represented. Also note that the string is empty of electrons; there are no numbers in the upper right angles (1s ² 2s ² 2p ⁶ …).

It should be remembered that s orbitals can "house" two electrons (ns ²). The p orbitals are three in total (look at the three boxes above), so they can accommodate six electrons (np ⁶). And finally, the d orbitals are five, and the f are seven, having a total of ten (nd ¹⁰) and fourteen (nf ¹⁴) electrons, respectively.

Electronic configuration abbreviation

Having said the above, we proceed to fill the previous row of quantum notations with electrons:

1s ² 2s ² 2p ⁶ 3s ² 3p ⁶ 4s ² 3d ¹⁰ 4p ⁶ 5s ² 4d ¹⁰ 5p ⁶ 6s ² 4f ¹⁴ 5d ¹⁰ 6p ⁶ 7s ² 5f ¹⁴ 6d ¹⁰ 7p ⁶

How many electrons are there in all? 118. And to which element does such a massive number of electrons correspond in its atom? To the noble gas oganeson, Og.

Suppose there is an element with a quantum number Z equal to 119. Then, its valence electron configuration would be 8s ¹; but what would its complete electronic configuration be?

1s ² 2s ² 2p ⁶ 3s ² 3p ⁶ 4s ² 3d ¹⁰ 4p ⁶ 5s ² 4d ¹⁰ 5p ⁶ 6s ² 4f ¹⁴ 5d ¹⁰ 6p ⁶ 7s ² 5f ¹⁴ 6d ¹⁰ 7p ⁶ 8s ¹

And what would your electronic kernel configuration be, the compact one? Is:

8s ¹

Note the obvious simplification or abbreviation. In the symbol all 118 electrons written above are counted, so this uncertain element has 119 electrons, of which only one is of valence (it would be located below francium in the periodic table).

Examples

general

Suppose now that you want to make the abbreviation progressively:

2s ² 2p ⁶ 3s ² 3p ⁶ 4s ² 3d ¹⁰ 4p ⁶ 5s ² 4d ¹⁰ 5p ⁶ 6s ² 4f ¹⁴ 5d ¹⁰ 6p ⁶ 7s ² 5f ¹⁴ 6d ¹⁰ 7p ⁶

Note that 1s ² was replaced by. The next noble gas is neon, which has 10 electrons. Knowing this, the abbreviation continues:

3s ² 3p ⁶ 4s ² 3d ¹⁰ 4p ⁶ 5s ² 4d ¹⁰ 5p ⁶ 6s ² 4f ¹⁴ 5d ¹⁰ 6p ⁶ 7s ² 5f ¹⁴ 6d ¹⁰ 7p ⁶

Then argon follows, with 18 electrons:

4s ² 3d ¹⁰ 4p ⁶ 5s ² 4d ¹⁰ 5p ⁶ 6s ² 4f ¹⁴ 5d ¹⁰ 6p ⁶ 7s ² 5f ¹⁴ 6d ¹⁰ 7p ⁶

Because the next noble gas is krypton, the abbreviation is advanced by another 36 electrons:

5s ² 4d ¹⁰ 5p ⁶ 6s ² 4f ¹⁴ 5d ¹⁰ 6p ⁶ 7s ² 5f ¹⁴ 6d ¹⁰ 7p ⁶

Xenon has 54 electrons, and therefore we move the abbreviation to the 5p orbital:

6s ² 4f ¹⁴ 5d ¹⁰ 6p ⁶ 7s ² 5f ¹⁴ 6d ¹⁰ 7p ⁶

By now you will have noticed that the electron configuration is always abbreviated to the np orbital; that is, the noble gases have these orbitals filled with electrons. And finally radon follows, with 86 electrons, so we abbreviate to the 6p orbital:

7s ² 5f ¹⁴ 6d ¹⁰ 7p ⁶

Oxygen

Oxygen has eight electrons, its complete electronic configuration being:

1s ² 2s ² 2p ⁴

The only abbreviation we can use is for 1s ². Thus, your electronic kernel configuration becomes:

2s ² 2p ⁴

Potassium

Potassium has nineteen electrons, its complete electronic configuration being:

1s ² 2s ² 2p ⁶ 3s ² 3p ⁶ 4s ¹

Note that we can use the symbol to abbreviate this configuration; as well as and. The latter is the one used because argon is the noble gas that comes closest to potassium. So your kernel electronics configuration looks like:

4s ¹

Indian

Indium has forty-nine electrons, its complete electronic configuration being:

1s ² 2s ² 2p ⁶ 3s ² 3p ⁶ 4s ² 3d ¹⁰ 4p ⁶ 5s ² 4d ¹⁰ 5p ¹

Since krypton is the closest noble gas preceding indium, the symbol is used for the abbreviation, and we have its kernel electron configuration:

5s ² 4d ¹⁰ 5p ¹

Although the 4d orbitals do not formally belong to the indium kernel, their electrons are not involved (at least under normal conditions) in its metallic bond, but rather those of the 5s and 5p orbitals.

Tungsten

Tungsten (or wolfram) has 74 electrons and its complete electron configuration is:

1s ² 2s ² 2p ⁶ 3s ² 3p ⁶ 4s ² 3d ¹⁰ 4p ⁶ 5s ² 4d ¹⁰ 5p ⁶ 6s ² 4f ¹⁴ 5d ⁴

Again, we look for the closest noble gas that precedes it. In your case, it corresponds to xenon, which has full 5p orbitals. So we replace the string of quantum notations with the symbol, and we will finally have its kernel electron configuration:

6s ² 4f ¹⁴ 5d ⁴

References

1. Shiver & Atkins. (2008). Inorganic chemistry. (Fourth edition). Mc Graw Hill.
2. Whitten, Davis, Peck & Stanley. (2008). Chemistry (8th ed.). CENGAGE Learning.
3. Pat Thayer. (2016). Electron Configuration Diagrams. Recovered from: chemistryapp.org
4. Helmenstine, Anne Marie, Ph.D. (December 05, 2018). Noble Gas Core Definition. Recovered from: thoughtco.com/
5. Wikipedia. (2019). Electronic configuration. Recovered from: es.wikipedia.org