# Is the shorthand electron configuration of Br- just [Kr]?

Is the shorthand electron configuration of $\ce{Br-}$ just $\ce{[Kr]}$?

Also what about $\ce{Ca^2+}$—is it just $\ce{[Ar]}$? And, is $\ce{Na+}$ just $\ce{[Ne]}$?

• I meant is Na+ just [Ne] – Karis Mar 18 '18 at 18:39
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You could render bromide ion that way. But the outermost electrons in the "krypton core" are potentially reactive, valence electrons; therefore $\text{[Kr]}$ is not an accurate description of how the electrons really act. Only the argon core acts like a noble gas, so you are better off rendering the bromide ion as $\text{[Ar]3d}^{10}\text{4s}^2\text{4p}^6$.
Cations stripped to the noble gas core, however, really are stripped to unreactive electrons, so calcium ion can accurately be rendered as $\text{[Ar]}$.