Question

Give the electronic configuration of an element $\mathrm{X}$ whose atomic number is $19$.

Answer 1

Electronic configuration:

1. The distribution of electrons in different shells or energy level of an atom is known as the electronic configuration.
2. Starting from the nucleus, the shells are named as $\mathrm{K},\mathrm{L},\mathrm{M},\mathrm{N}$ and so on.
3. The maximum capacity of $\mathrm{K}$ shell is to hold $2$ electrons, that of $\mathrm{L}$ shell is to hold $8$ electrons, that of $\mathrm{M}$ shell is to hold $18$ electrons and that of $\mathrm{N}$ shell is to hold $32$ electrons.

Electronic configuration of an element $\mathrm{X}$ whose atomic number is $19$:

1. The atomic number of element $\mathrm{X}$ is $19$.
2. Number of electrons in an atom is equal to the atomic number. Thus, element $\mathrm{X}$ has $19$ electrons.
3. In an atom of element $\mathrm{X}$, the $\mathrm{K}$ shell has $2$ electrons and the $\mathrm{L}$ shell has $8$ electrons. Thus, $10$ electrons are filled.
4. Now, the remaining $9$ electrons should go in the $\mathrm{M}$ shell.
5. But according to Bohr Bury scheme, the outermost shell cannot have more than $8$ electrons.
6. Thus, $8$ electrons go in the $\mathrm{M}$ shell and the remaining $1$ electron goes in the $\mathrm{N}$ shell.
7. Thus, the electronic configuration is $\left(2,8,8,1\right)$.

Thus, the electronic configuration of an element $\mathrm{X}$ whose atomic number is $19$ is $\left(2,8,8,1\right)$.