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The orbital diagram (also called an energy diagram) is another way of writing the electronic configuration of an element, but representing the electrons with small arrows and the orbitals with small horizontal lines or boxes.
A single orbital cannot contain more than 2 electrons of opposite spin. And each subshell contains a certain number of orbitals:
We must remember that there are 7 energy levels: 1, 2, 3, 4, 5, 6 and 7. And each of them has, in turn, up to 4 energy sublevels called s, p, d and f.
Each sublevel contains a certain number of orbitals:
In an energy level diagram these shells and subshells are represented as follows:
To know how to draw orbital diagrams, we must first know the Aufbau principle, the Pauli exclusion principle and Hund’s rule.
The Aufbau Progressive Filling Principle states that electrons occupy the lower energy orbitals, and progressively fill the higher energy orbitals.
Within each energy level, the s sublevel has lower energy than the p sublevel, which has lower energy than the d sublevel, and so on. However, it must be taken into account that within a set of orbitals all have the same energy. For example, all the orbitals that make up the 2p subshell have the same energy. Often these orbitals are represented by a box or series of boxes, which can be arranged in order to show the increase in energy.
Also, we sometimes find it easy to differentiate between the three orbitals that make up the p subshell, referring to them as px, py, and pz.
For the first 18 elements, the electrons occupy the orbitals starting with the one with the lowest energy and fill their capacity before starting the next one. So the 1s orbital is filled with two electrons, then the 2s is filled with two electrons, then the 2p is filled with six electrons, the 3s is filled with two, and finally the 3p is filled with six.
After the 3p subshell there is an energy overlap, this is how we find that before the 3d orbitals are filled the electrons enter the 4s orbital. The same goes for the 5s and 4d. At higher energy levels there is more overlap of this type.
The Pauli exclusion principle states that each orbital cannot contain more than two electrons. Each electron must have a different spin, which is indicated by different symbols.
The Hund’s rule says that electrons will fill empty orbitals within their energy level before joining another electron.For any set of orbitals, such as 2p orbitals, one electron is found to be in each orbital before pairing occurs.Apparently it takes less energy for an electron to occupy an orbital on its own than it does to pair with another electron in an orbital of equal energy.
Knowing the three rules, we will show how to draw the orbital diagram for oxigen.
Take a moment to draw the orbital diagram in white.
Now we present examples of orbital diagrams of some elements. All the examples have been created with the help of the Electron Orbital Diagram Generator.