General Rules on Writing e- Configurations [ENDORSED]

[Junghyuk_Park_1I]

I had the following question about writing electron configurations. I know during lecture Dr. Lavelle stated that once the d orbital becomes available for an element, the electron placement on the configuration short hand notation does not simply fill in order (i.e. [Ar] 4s^2 3d^3 vs. [Ar] 3d^5). I was wondering what the general rules were for filling in the electron shells to create the greatest stability? So far I've heard people tell me that it is when half or an entire orbital (s, p, d, f, etc.) should be filled for the greatest stability. Is this true and are there any other general rules to follow? What does one do if the 2 e- in the s orbital are filled, but only an 6 e- are filled in the d orbital? Would the electrons stay in the s orbital or move to the d orbital? Thanks in advance!

[Nerissa_Low_2F]

So, when we write electron configurations, we fill in electrons for elements based on their order in the periodic table. This is the only "general rule" to follow. When the d orbital becomes available, you would still fill the 4s first, and then proceed filling those in the d orbital. The only exceptions to this rule is Chromium and Copper. For these elements, they take one electron from the 4s orbital to place in their 3d orbital, so that for Chromium it has a half full orbital with every suborbital having 1 electron due to Pauli Exclusion Principle, and for Copper it has 1 full 3d orbital. Both Copper and Chromium would then have a 4s orbital with 1 electron.

So, if you were to have 2 electrons in the s orbital and 6 in the d orbital, The element would be Iron. The electron configuration would be [Ar] 3d6 4s2.

[Jocelyn Sandoval 3B]

Well if you are looking for "general rules", it would be best to follow Hund's Rule and the Aufbau Principle because they tell you how you should be filling in the orbitals, which will make it easier for you to write the electron configuration.