Exceptions for electron configuration

[Danielle DIS2L]

How come Cr(Chromium) and Cu(Copper) are an exceptions for electron configurations?

[Katie Lam 2J]

Chromium is an exception because, if you were to do the electron configuration normally, you would get [Ar]3d^4 4s^2. However, a half full d orbital is more stable. Therefore, the electron configuration will be [Ar]3d^5 4s^1. Copper is an exception because, if you were to do the electron configuration normally, you would get [Ar]3d^9 4s^2. However, a full d orbital is more stable. Therefore, the electron configuration will be [Ar]3d^10 4s^1. Hope this helps!

[Yu Jin Kwon 3L]

Katie said it perfectly! To add on, all the elements in group 6 and group 11 exhibit this exception. Although we might not have to know that for this midterm, it's nice to keep in the back of our minds to understand why Cr and Cu are exceptions :)

[rhettfarmer-3H]

I think for this question it is very important to remember that there are certain rules that must be remembered. One of which is the energy levels the D block has more energy than the s block therefore, when we fill the d block rather than filling the s block the element becomes more stable. Similar to why we leave an s block not fully covered.