Question

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

Answer 1

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

(That, however, changes when we get to `"Sc"`.)

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Under the so-called KLMN notation,

`K := 1s`

`L := {2s, 2p}`

`M := {3s, 3p, 3d}`

`N := {4s, 4p, 4d, 4f}`

And since the `4s` orbital is singly occupied in potassium, the KLMN notation for `"K"` is

`barul(|stackrel(" ")(" ""K": overbrace(2)^(1s^2)" "overbrace(8)^(2s^2 2p^6)" "overbrace(8)^(3s^2 3p^6)" "overbrace(1)^(4s^1)" ")|)`

Likewise for `"Ca"`...

`barul(|stackrel(" ")(" ""Ca": overbrace(2)^(1s^2)" "overbrace(8)^(2s^2 2p^6)" "overbrace(8)^(3s^2 3p^6)" "overbrace(2)^(4s^2)" ")|)`