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, …….
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.
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.
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.
Check out the structure of NH3 here
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