Question

How do you fill electron orbitals?

Answer 1

We know that the filling of electrons in the orbitals is termed as electronic configuration. There are three principles which we must follow while assigning electrons to the orbitals, they are, Aufbau principle, Hund’s rule and Pauli’s exclusion principle.

Complete step by step answer:
Let’s discuss all the three principles one by one.
The Aufbau principle states that in the ground state of an atom, the electrons are added progressively to the various orbitals in increasing order of energies starting from the orbital of lower energy.
The increasing order of energies of various orbitals is:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 4d, 5p……
Let’s understand Pauli’s exclusion principle. According to this principle an orbital can have a maximum of two electrons and their spins are opposite.
Now, we discuss Hund’s rule of maximum multiplicity. According to this rule, when more than one orbitals of equal energy are available, the electrons will first occupy these orbitals with parallel spins. The pairing of electrons will then take place.
Let’s understand with the help of an example. We know the atomic number of oxygen is 8. Now, we will fill orbitals of oxygen.
We fill the electrons in the orbitals following the above three principles.

The electronic configuration of oxygen is$1{s^2}2{s^2}2{p^4}$. All the orbitals have a maximum of two electrons that means Pauli’s exclusion principle is followed. Electrons are filled as in the increasing order of energies of orbitals that means the Aufbau principle is followed. Electrons are first assigned as parallel spins that means Hund’s rule is followed.

Note: The ground state of an atom is defined as the state of an atom when all the present electrons occupy their lowest energy levels as required by their n and l values. It is to be noted that since the ground state of an atom is the most stable, the electronic distribution relates to ground state only.