Electron configuration

Question

what is the shorthand electron configuration of a potassium ion?

- [Ne]3s²3p⁶

- [Ne]3p⁸

- [He]3p⁶

- [He]3s²3p⁵

- [He]3s³3p⁴

 

Answer 1

I assume you mean a POSITIVE potassium ion, K⁺.  Find K in the periodic table.  Its atomic number is 19.  Subtract 1 electron to get K⁺.  The ion will behave similarly to an atom of atomic number 18.  Find the nearest noble gas that precedes Z=18 in the periodic table.  That is Ne, with 10 electrons.  Add electrons until you reach 18.  Note that with 10 electrons, 

 

[Ne] = 1s²2s²2p⁶

 

The n=1 and n=2 shells are filled, so you have to start filling the n=3 shell, until you are up to 18 electrons total.  Add 8 electrons and get a configuration of

 

[Ne]3s²3p⁶.