Question

Calculate the number of electrons in sulphur having $n + l = 3$
A.2
B.4
C.6
D.8

Answer 1

The atomic number of sulphur is 16. The electronic configuration of sulphur can be written as $1{s^2}2{s^2}2{p^{^6}}3{s^2}3{p^4}$ . n is the principal quantum number. It tells the energy level in which an electron is present. It can be represented by the numbers 1, 2, 3, 4.. corresponding to shells K, L, M, N. $l$ is the azimuthal quantum number. It can have possible values from 0, 1, 2, 3, to $n - 1$ corresponding to K, L, M, N

Complete step by step answer:
We know the electronic configuration of Sulphur.
-Now we will individually find for which orbital the value of $n + l = 3$ .
For $1{s^2}$ the value of the principal quantum number is equal to 1 and for s, the azimuthal quantum number is zero.
Hence, $n + l = 1 + 0 = 1$
-For $2{s^2}$ , the value of the principal quantum number is equal to two and the azimuthal quantum number is zero.
Hence, $n + l = 2 + 0 = 2$ so this is rejected.
-For $2{p^6}$ , the value of the principal quantum number is equal to two and the azimuthal quantum number is equal to one.
So, $n + l = 2 + 1 = 3$
-For $3{s^2}$ the value of the principal quantum number is equal to three and the azimuthal quantum number is equal to zero. So $n + l = 3 + 0 = 3$ which is accepted
-For $3{p^4}$ the value of the principal quantum number is equal to three and the azimuthal quantum number is equal to one.
-So $n + l = 3 + 1 = 4$ which is not accepted.
-So the total number of electrons having $n + l = 3$ is in $2{p^6}$ and $3{s^2}$. Therefore, the number of electrons is $6 + 2 = 8$ electrons.

Hence, the correct answer is option D..

Note:
Principal quantum number determines the energy level and the size of the shells. It has positive integer values. The Azimuthal quantum number is also called angular momentum. It helps in determining the orbital shape. Magnetic quantum numbers are also denoted as m and it determines the orbital orientation. Spin quantum number determines the spin orientation.