Question

The atom of an element has $20$ protons, $20$ neu­trons, and $20$ electrons. Find out its electronic configuration mentioning the shell.

Answer 1

Given:

Number of protons$=20$

Number of neutrons$=20$

Number of electrons$=20$

Formula used:

Atomic number$=$Number of protons$=$Number of electrons

Find the atomic number of the element:

Atomic number$=$Number of protons$=$Number of electrons

Atomic number$=20$

Thus, the atomic number of the element is $20$.

Find the name of the element:

The element with atomic number $20$ is Calcium $\mathbf{\left(}\mathbf{Ca}\mathbf{\right)}$.

Thus, the name of the element is Calcium $\mathbf{\left(}\mathbf{Ca}\mathbf{\right)}$.

Write the electronic configuration of Calcium:

1. The distribution of electrons in various energy levels or shells of an atom of the element is known as its electronic configuration.
2. The total number of electrons in Calcium atom is $20$.
3. Starting from the nucleus, the first shell i.e.$\mathrm{K}$ shell holds $2$ electrons, the second shell i.e.$\mathrm{L}$ shell holds $8$ electrons. Thus, $10$ electrons are filled.
4. Now, the third shell i.e. $\mathrm{M}$ shell is expected to hold the remaining $10$ electrons.
5. But according to Bohr Bury scheme, the outermost shell cannot hold more than $8$ electrons.
6. Thus, the $\mathrm{M}$ shell holds $8$ electrons and the remaining $2$ electrons go into the fourth shell i.e. $\mathrm{N}$ shell.
7. Thus, the electronic configuration is $(2,8,8,2)$.