How many electrons in sulphur ( Z = 16 ) can have n + l = 3 ?
The electronic configuration of sulphur is as follows: 1s2 2s2 2p6 3s2 3p4. As Sulphur is in the third period, p block, n = 3,
ℓ =1.
Sulphur At no. =16; electronic config: 2s2 2p6 3s2 3p4. Sulphur is in the third period, p block. Recalling that the number of the p sublevels corresponds to the period number, the principle quantum no., n = 3. The highest energy electron would be the 16th electron which is the final electron (3p4). A p sublevel means angular quantum no., ℓ = 1.
Let us check for no. of electrons in sulphur having n+ℓ=3
For all 1s, 2s sublevels n=1,2 but ℓ=0(as ‘s’ is the subshell), therefore n+ℓ cannot be 3 (i.e. 1+0, 2+0 cannot be 3).
But for 3s sublevels n= 3 and ℓ=0, therefore n+ℓ = 3+0 =3(satisfies the condition). There are 2 electrons in 3s subshell.
Next consider 2p sublevel where n= 2 and ℓ=1(as ‘p’ is the sub shell), therefore n+ℓ = 2+1 =3 (satisfies the condition). There are 6 electrons in the 2p subshell.
For 3p sublevel where n=3 and ℓ=1, n+ℓ = 3+1 cannot be 3.
Therefore totally 8 electrons 3s subshell (with 2 electrons) and 2p subshell (with 6 electrons) satisfy n+ℓ = 3 in sulphur.