Why are Noble Gas symbols often included in the electronic configuration of certain elements?

1 Answer
Jun 29, 2017

Answer:

Well, it gives the configuration of the last Noble Gas.......

Explanation:

For the full electronic configuration of calcium, #Z=20#, I could write out........

#1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)4s^(2)#.....

But of course this a portmanteau of the LAST Noble gas, #"argon,"# #Z=18#, whose electronic configuration is the closed-shell....

#1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)#.....PLUS 2 extra valence electrons that fill the #4s# shell. The use of #[Ar]# to represent this closed-shell, inner core of electrons is perfectly acceptable, and widespread.....

And so...

#underbrace(1s^(2)2s^(2)2p^(6)3s^(2)3p^(6))_"electronic configuration of argon"4s^(2)#.....#-=# #[Ar]4s^2#

How would I represent the electronic configuration of #Na?#