# Finding electron configuration by following the Aufbau principle

In the question, "Electron Configuration of Tellurium", there is mention of the 'follow yellow brick road' method of finding electron configuration.

What I'd learned in the past was to find the nearest noble gas (in the row above the element of interest) and count from there.

I searched in Google for this method and see that it appears to also called the Aufbau principle & diagonal method. However I'm not getting a good grasp on how it works.

Could someone explain this method to me?

Also, would this method work for something with a weird electron configuration, like copper?

• I think the more common name is to follow the aufbau principle. – Jan Dec 1 '16 at 18:57
• – Pritt says Reinstate Monica Apr 25 '17 at 15:36

## 1 Answer

The so-called rule is to fill the subshells in increasing order of $n+l$. For subshells with the same value of $n+l$, the subshell with lowest $n$ is filled first.

$$\begin{array}{cc} \hline n+l & \text{Orbitals} \\ \hline 1 & \mathrm{1s} \\ 2 & \mathrm{2s} \\ 3 & \mathrm{2p,3s} \\ 4 & \mathrm{3p,4s} \\ 5 & \mathrm{3d,4p,5s} \\ \vdots & \vdots \\ \hline \end{array}$$

For all intents and purposes, this is exactly equivalent to your heuristic of "go from the nearest noble gas", since to get the configuration of the noble gas itself you have to go through this same ordering of subshells. You can easily verify that the table above reproduces the order of filling of the Periodic Table.

Chromium and copper are exceptions to the rule (obviously there are many more).