I am trying to calculate the effective nuclear charge on a outermost electron of a potassium ion (K^{+}).

How many core electrons are in a potassium ion?

I just need to check this, I think it is 10.

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My solution

Z_{eff}=Z-s

Where Z=protons

and s=core electrons

I believe the number of core electrons is 10 because in a neutral atom of potassium there is 19 electrons and 18 core electrons. Shell 4 where 1 electron originally was becomes 0 when it is a potassium ion. Therefore by removing electron one, the core electrons are the 10 in shell 1 and 2 and 8 is in our outermost shell (not valence).

Z_{eff}=19-10=**9+**

The effective nuclear charge on the outermost electron in a potassium ion will be 9+.

Logically this makes sense because in Argon, the Z_{eff}=8+ and because potassium has one additional proton, it should be higher, electron configuration is the same in the potassium ion and argon.

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Did I do this right?

Thanks in advance