How To Fill The Electronic Configuration Of Elements

Electronic configuration is the arrangement of electrons in the atomic orbital. Here, are the rules to write the configuration of electron in the atomic orbital.

Rules for filling electronic configuration in an atomic orbital

There are some rules to fill the electronic configuration in an element. Let’s discuss them one by one :

Aufbau Principle for filling electronic configuration in an atomic orbital

In the ground state of the atoms, the orbitals are filled in order of increasing energies. The increasing order of the energies of the orbitals is : 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d,7p, …….

Electronic configuration according to Aufbau Principle @basicsofchemistry

Alternatively, follow the ( n + l ) rule. This is the sum of principle quantum number (n) and azimuthal quantum number (l) It states that electrons are filled in the increasing ( n + l ) values.

Electronic configuration according to ( n + l ) rule @basicsof chemistry

Pauli Exclusion Principle for filling electron configuration in an atomic orbital

No 2 electrons can have 4 equal set of quantum numbers. Spin quantum number must be different for 2 electrons in an orbital. If one electron has clockwise spin then the other is anticlockwise. ( i.e. +1/2 and – 1/2 )

Hund rule of Maximum multiplicity for filling electron configuration in an atomic orbital

Pairing of electrons in an orbital in the given sub shell will not occur until all the electrons are singly filled in each orbital. See the configuration of N in the example below.

Rules for filling electronic configuration : Pauli Exclusion Principle and Hund rule of maximum multiplicity @basicsofchemistry

Exceptional electronic configurations of Cu and Cr

There are some elements which don’t follow the given set of rules like Cu and Cr. These elements show half filled and full filled stability. The reasons are symmetrical distribution and exchange energy. Symmetry leads to stability. Therefore, d5 and d10 are more stable configurations.

The energy released during the exchange is called exchange energy. More the exchange energy , more will be the stability.

Exceptional electronic configuration of Cr and Cu @basicsofchemistry

Check out the structure of NH3 here

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