Electron configuration of an element shows us how the electrons are distributed in its atomic orbitals.
The electron configurations of atoms follow a standard notation in which all the atomic subshells that contain electrons (with the number of electrons they hold written in superscript) are placed in a certain sequence.
For example, the atomic number of Sodium is 11 and its electron configuration is .
Aufbau principle:-
The Aufbau principle states how the electrons are filled in their atomic orbitals of an atom that is in its ground state.
The principle states that electrons are filled into the atomic orbitals in the increasing order of the orbital energy level.
According to the Aufbau principle, the available atomic orbitals which have the lowest energy levels are occupied before those which have higher energy levels.
A diagram is given below which illustrates us the order in which atomic orbitals are filled:
Here, refers to the principal quantum number whereas, refers to the azimuthal quantum number.
When it is the s-orbital, when it is the p-orbital, when it is the d-orbital and when it is the f-orbital
Electronic configuration of Nickel:-
Atomic number of Nickel is 28, that is Nickel has a total of 20 electrons.
Since 1s orbital can hold a maximum of 2 electrons, so first 2 electrons will fill the 1s orbital, and the next 2 electrons will fill the 2s orbital.
The next six electrons of Calcium will go in the 2p orbital, as the p orbital can hold up to six electrons.
The 2p orbital will be completely filled with six electrons and after that, the next two electrons will move up to fill the 3s orbital.
Similarly in the same fashion, the next 6 electrons will fill up the 3p orbital.
Again the, 2 electrons will be placed in the 4s orbital.
And lastly, the remaining 8 electrons will be placed in the 3d orbital, as the d-orbital can accommodate up to 10 electrons.
Therefore, the electronic configuration of Nickel in the ground state is.
But here it is asked to write the electronic configuration of , which means it has 2 electrons less.
Now, these 2 electrons will be removed during a reaction from the outermost 4s orbital, rather than the 3d orbital.
Now the new electronic configuration of is
This filling up of the orbitals with electrons is according to the Aufbau principle.
Therefore, the electronic configuration of according to the Aufbau principle can be written as.