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

Jun 29, 2017

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

#### Explanation:

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

$1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 4 {s}^{2}$.....

But of course this a portmanteau of the LAST Noble gas, $\text{argon,}$ $Z = 18$, whose electronic configuration is the closed-shell....

$1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6}$.....PLUS 2 extra valence electrons that fill the $4 s$ shell. The use of $\left[A r\right]$ to represent this closed-shell, inner core of electrons is perfectly acceptable, and widespread.....

And so...

${\underbrace{1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6}}}_{\text{electronic configuration of argon}} 4 {s}^{2}$.....$\equiv$ $\left[A r\right] 4 {s}^{2}$

How would I represent the electronic configuration of Na?