The distribution of electrons into orbitals of an atom is called its electronic configuration.
The electronic configuration of different atoms can be represented in two ways.
For example :
(i) sapbdc...... notation
(ii) Orbital diagram
In the first notation, the subshell is represented by the respective letter symbol and the number of electrons present in the subshell is depicted, as the super script, like a, b, c, ... etc. The similar subshell represented for different shells is differentiated by writing the principal quantum number before the respective subshell. In the second notation each orbital of the subshell is represented by a box and the electron is represented by an arrow (↑) a positive spin or an arrow (↓) a negative spin. The advantage of second notation over the first is that it represents all the four quantum numbers.
The hydrogen atom has only one electron which goes in the orbital with the lowest energy, namely 1s. The electronic configuration of the hydrogen atom is 1s 1 meaning that it has one electron in the 1s orbital. The second electron in helium (He) can also occupy the 1s orbital. Its configuration is, therefore, 1s 2 . As mentioned above, the two electrons differ from each other with opposite spin, as can be seen from the orbital diagram.
The orbital picture of these elements can be represented as follows:
As shown above , nitrogen is having half filled orbital and Neon is having fully filled orbital therefore they are more stable than the rest of above elements .
Since neon is having fully filled orbital , it is the most stable and least reactive element . It is also termed as noble gases or inert gases .
The electrons in the completely filled shells are known as core electrons and the electrons that are added to the electronic shell with the highest principal quantum number are called valence electrons
Condensed Electron Configurations
Stability of half-filled and fully filled orbitals –
The completely filled and completely half-filled subshells are stable due to the following reasons:
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Symmetrical distribution of electrons |
The completely filled or half filled subshells have symmetrical distribution of electrons in them and are therefore more stable. Electrons in the same subshell have equal energy but different spatial distribution. Consequently, their shielding of one another is relatively small and the electrons are more strongly attracted by the nucleus |
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Exchange Energy |
The stabilizing effect arises whenever two or more electrons with the same spin are present in the degenerate orbitals of a subshell. These electrons tend to exchange their positions and the energy released due to this exchange is called exchange energy. The number of exchanges that can take place is maximum when the subshell is either half filled or completely filled .As a result the exchange energy is maximum and so is the stability.
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