What is the electron configuration of Sr2+?

##1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10)4s^(2)4p^(6)##

Strontium is 38 so its can be written:

##2.8.18.8.2##

In orbital notation this is:

##1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10)4s^(2)4p^(6)5s^(2)##

The notation is:

##[Kr]5s^(2)##

When strontium forms a 2+ ion the 2 outer ##5s## electrons are lost so ##Sr^(2+)## can be written as:

##1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10)4s^(2)4p^(6)##

Or:

##[Kr]##