I was given a question where I had to write the orbital notation of Osmium (Os) and I got it wrong.

The question:

6s2 --> ↑↓ 4f --> ↑↓↑↓↑↓↑↓↑↓↑↓↑↓ 5d6 --> ↑↓↑↓↑↑

The arrows above are my answer. What did I do wrong? I think it might be my answer to 5d6 but I am not sure. How many unpaired electrons are in Osmium?


According to Hund's rule of Maximum Multiplicity, a higher spin multiplicity is more stable. In simple terms, this means that a given atom would try to have the maximum number of unpaired electrons. For Osmium, which has a $\mathrm{5d^6}$ configuration, there are 5 d-orbitals and 6 electrons to fill, so the maximum number of unpaired electrons in this arrangement would be 4 (two electrons pair up and occupy one orbital, and the remaining 4 occupy a single orbital each). Here's the orbital diagram (taken from this Chemistry Libretexts article, which you should read)

Osmium orbital diagram


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