# 2.6: Writing Electron Configurations

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- 213215

In the previous section, the following electron configuration was generated. Recall that this notation can be used to explicitly state the location of individual electrons within the first six orbitals/orbital sets of an atom.

1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}

When applying this pattern, two rules must be followed:

- In order to maximize their stability, electrons will always prefer to occupy the lowest energy orbital that is available. Therefore, the energy level/orbital combinations given within the electron configuration should be filled
*in the order shown above*, beginning with the "1s" energy level/orbital combination. - The number of electrons assigned to each energy level/orbital combination should never exceed the maximum indicated by the superscript. If an atom contains more electrons than what that energy level/orbital combination can hold, fill the next energy level/orbital combination in the configuration, until all electrons have been placed.

For example, consider an atom of sulfur.

In order to establish the location of sulfur's electrons, the total number of electrons in an atom of sulfur (S) must first be determined. Recall that the number of protons and electrons in an atom must be equal, in order for that atom to have an overall neutral charge. Furthermore, the number of protons present in an atom is defined by the element's atomic number. Therefore, since sulfur has an atomic number of 16, an atom of sulfur contains 16 protons and *16 electrons*.

The location of each of sulfur's electrons can then be determined by applying the given electron configuration pattern until the superscripts total to 16. Based on the rules given above, the "1s" energy level/orbital combination must be filled first. However, all 16 electrons cannot be placed in the "1s" orbital, since the maximum number of electrons indicated by its superscript is 2. Therefore, this energy level/orbital combination is completed by filling it to its maximum capacity, as follows:

1s^{2}

Since sulfur still has 14 additional electrons that must be placed, the next energy level/orbital combination, the "2s" orbital, must be filled. However, all 14 electrons cannot be placed in the "2s" orbital, since the maximum number of electrons indicated by its superscript is 2. Therefore, this energy level/orbital combination is completed by filling it to its maximum capacity, as follows:

1s^{2}2s^{2}

Sulfur still has 12 additional electrons that must be placed, so the next energy level/orbital combination, the "2p" orbital, must be filled, but all 12 electrons cannot be placed in the "2p" orbital, since the maximum number of electrons indicated by its superscript is 6. Therefore, this energy level/orbital combination is completed by filling it to its maximum capacity, as follows:

1s^{2}2s^{2}2p^{6}

Sulfur still has 6 additional electrons that must be placed, so the next energy level/orbital combination, the "3s" orbital, must be filled. However, all 6 electrons cannot be placed in the "3s" orbital, since the maximum number of electrons indicated by its superscript is 2. Therefore, this energy level/orbital combination is completed by filling it to its maximum capacity, as follows:

1s^{2}2s^{2}2p^{6}3s^{2}

Sulfur still has 4 additional electrons that must be placed, so the next energy level/orbital combination, the "3p" orbital, must be filled. In this case, all 4 electrons *can *be placed in the "3p" orbital, since the maximum number of electrons indicated by its superscript is 6. Therefore, these 4 electrons are assigned to the "3p" orbital, as follows:

1s^{2}2s^{2}2p^{6}3s^{2}3p^{4}

Since all of sulfur's electrons have been placed, this final entry represents sulfur's electron configuration.