# How do you write the electron configuration for the following ions?

## K^+1 Br-1 Al+3 As-3?

Dec 21, 2017

K^+, Z=19; 1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)...

...the $4 {s}^{1}$ electron is lost upon ionization.....

#### Explanation:

Br^-, Z=35; 1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10)4s^(2)4p^6...

...the $4 p$ electron is FILLED upon ionization.....

Al^(3+), Z=13; 1s^(2)2s^(2)2p^(6)...the $3 s$ and $3 p$ electrons have been lost....

As^(3-), Z=33; 1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10)4s^(2)4p^6...and note that this configuration is the same as that of $B {r}^{-}$, i.e. isoelectronic with krypton....