Theoretically electronic configuration and number of unpaired electron can be found out by using molecular orbital theory. But, practically I have seen only up to 20. For example, for Ne2enter image description here

But for S2 (32 electrons) how to find out the electronic configuration and number of unpaired electrons.


The molecular orbital energy-level diagram of $\ce{S2}$ is given below:-enter image description here


We can see how close the energy the 3s and 3p atomic orbitals are because their energy separation will determine whether the $\ce{π_3_{p}_{x,y}}$, or the $\ce{σ_{3}_{p}_{z}}$ molecular orbital is higher in energy. Because the ns–np energy gap increases as the nuclear charge increases , the $\ce{σ_{3}_{p}_{z}}$ molecular orbital will be lower in energy than the $\ce{π_3_{p}_{x,y}}$ pair.

Each sulfur atom contributes 6 valence electrons, for a total of 12 valence electrons. Ten valence electrons are used to fill the orbitals through $\ce{π_{3}_{p}_{z}}$and $\ce{π_3_{p}_{y}}$, leaving 2 electrons to occupy the degenerate $\ce{π^{⋆}_{3}_{p}_{z}}$ and $\ce{π^{⋆}_{3}_{p}_{y}}$ pair. From Hund’s rule, the remaining 2 electrons must occupy these orbitals separately with their spins aligned. With the numbers of electrons written as superscripts, the electron configuration of $\ce{S2}$ is $\ce{(σ_{3}_{s})^{2}(σ^{⋆}_{3}_{s})^{2}(σ_{3}_{p}_{z})^{2}(π_{3}_{p}_{z,y})^{4}(π_{3}_{p}^{⋆}_{x,y})^{2}}$ with 2 unpaired electrons at the antibonding $\ce{π^{⋆}}$ orbital and thus is paramagnetic. The bond order is (8 − 4) ÷ 2 = 2, so we predict an $\ce{S=S}$ double bond.

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