The element potassium has an atomic number 19 and a mass number is 39. Give the number of electrons, protons, and neutrons in it. Give the electronic configuration in different energy shells. Mention its valency.

Given:

Atomic number of Potassium $\mathbf{\left(}\mathbf{K}\mathbf{\right)}=19$

Mass number of Potassium $\mathbf{\left(}\mathbf{K}\mathbf{\right)}=39$

Formula:

1. Atomic number$=$Number of electrons$=$Number of protons
2. Mass number$=$Number of protons$+$Number of neutrons

Calculate the number of electrons in Potassium atom $\mathbf{\left(}\mathbf{K}\mathbf{\right)}$:

Number of electrons$=$Atomic number

Thus,

Thus, the number of electrons in Potassium is $19$.

Calculate the number of protons in Potassium atom $\mathbf{\left(}\mathbf{K}\mathbf{\right)}$:

Number of protons$=$Atomic number

Thus,

Thus, the number of protons in Potassium is $19$.

Calculate the number of neutrons in Potassium atom $\mathbf{\left(}\mathbf{K}\mathbf{\right)}$:

Mass number$=$Number of protons$+$Number of neutrons

Number of neutrons$=$Mass number$-$Number of protons

Number of neutrons$=39-19$$=20$

Thus, the number of neutrons in Potassium is $20$.

Electronic configuration of Potassium atom $\mathbf{\left(}\mathbf{K}\mathbf{\right)}$:

1. The number of electrons in Potassium is $19$.
2. In the potassium atom, the first shell i.e. $\mathrm{K}$ shell will hold $2$ electrons, the second shell i.e. $\mathrm{L}$ shell will hold $8$ electrons. Thus, $10$ electrons are filled.
3. Now, the third shell i.e. $\mathrm{M}$ shell is expected to hold the remaining $9$ electrons.
4. But according to Bohr Bury scheme, the outermost shell cannot have more than $8$ electrons.
5. Thus, the third shell i.e. $\mathrm{M}$ shell will hold $8$ electrons and the $1$ remaining electron goes to the fourth shell i.e. $\mathrm{N}$ shell.
6. Thus, the electronic configuration becomes $(2,8,8,1)$.

Thus, the electronic configuration of Potassium atom $\mathbf{\left(}\mathbf{K}\mathbf{\right)}$ is $(2,8,8,1)$.