# What are the KLMN notations for "K" and "Ca"? Why is the third digit no greater than 8 for these elements???

Jul 25, 2017

Because there is no need for potassium or calcium to use $3 d$ orbitals, which would have contained up to $10$ remaining electrons in the $M$ "shell". For $\text{K}$ and $\text{Ca}$ specifically, their $3 d$ orbitals are currently higher in energy than the $4 s$.

(That, however, changes when we get to $\text{Sc}$.)

Under the so-called KLMN notation,

$K : = 1 s$

$L : = \left\{2 s , 2 p\right\}$

$M : = \left\{3 s , 3 p , 3 d\right\}$

$N : = \left\{4 s , 4 p , 4 d , 4 f\right\}$

And since the $4 s$ orbital is singly occupied in potassium, the KLMN notation for $\text{K}$ is

$\overline{\underline{| \stackrel{\text{ ")(" ""K": overbrace(2)^(1s^2)" "overbrace(8)^(2s^2 2p^6)" "overbrace(8)^(3s^2 3p^6)" "overbrace(1)^(4s^1)" }}{|}}}$

Likewise for $\text{Ca}$...

$\overline{\underline{| \stackrel{\text{ ")(" ""Ca": overbrace(2)^(1s^2)" "overbrace(8)^(2s^2 2p^6)" "overbrace(8)^(3s^2 3p^6)" "overbrace(2)^(4s^2)" }}{|}}}$