Question

Write the electronic configuration of Lithium ($3Li$)

Answer 1

Hint: Electronic Configuration is the arrangement of electrons within an atom. The electronic configuration shows the position of electrons inside an atom.

Complete step by step answer:
While writing an electronic configuration of an element, the electrons of the first s-orbital are written first followed by the first p-orbital and so. Once the first orbital is filled up then the second orbital starts filling and this goes on like this till all the electrons are filled up in the respective orbital.
In case of Lithium ($Li$), we see that it has only $3$ electrons thus occupying only the first and second s-orbital. Thus occupying the whole 1s orbital and half filling the 2s orbital. Thus the electronic configuration will be- $1{s^2}2{s^1}$.
From this electronic configuration, we can see that the 1s-orbital is completely filled up. This can be seen in the case of Helium ($He$) also whose atomic number is 2 and thus electronic configuration becomes $1{s^2}$. Hence we can also write the electronic configuration of elements according to their nearest noble gases. In this case it will become- $\left[ {He} \right]2{s^1}$ .
We just replace the electronic configuration of the nearest noble gas with the symbol of that noble gas and continue the rest of the configuration like the original sequence.

Hence we can simply write the electronic configuration of Lithium as $[He]2{s^1}$.

Note: We can also write the electronic configuration of ions in the similar manner. For Lithium ion it will be $L{i^ + }$ , having 1 electron deficit. Now this electronic configuration becomes the same as that of Helium and the electronic configuration will be $1{s^2}$ or simply$[He]$.