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So I saw in some internet site that $\ce{SeS2}$ is a polar molecule. When I drew the Lewis structure of the molecule, it showed up as a linear molecule like this:

$$\ce{S=Se=S}$$

The electronegativity difference of $\ce{Se-S}$ is just $0.01$ and the linear form shows that vectors cancel each other. Yet, some websites state that this molecule is polar, when everything to me indicates is a non-polar molecule.

Are they wrong or am I missing something here?

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    $\begingroup$ Selenium disulfide has a composition that approximates to SeS2 and is sometimes called selenium sulfide. However, as used in proprietary formulations, it is not a pure chemical compound but a mixture where the overall Se:S ratio is 1:2. The compounds are Se–S rings containing a variable number of S and Se atoms, SenS8−n. en.wikipedia.org/wiki/Selenium_disulfide $\endgroup$ – Poutnik Dec 6 '20 at 8:04
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I understand your assumption of selenium disulfide being a simple molecular like that. It is similar to the mistake of silicon dioxide, which at first glance we might assign it to be a linear molecule like carbon dioxide. However the crystal structure of silicon dioxide is far more complex.

In selenium disulfide, the selenium and sulfur atoms form a 8-membered ring, similar to the 8-member rings you would find in certain allotropes of either elemental selenium or elemental sulfur. The ratio of Se:S atoms is not exactly 1:2 as the chemical formula implies (that would give 8/3 atoms of Se and 16/3 atoms of S per ring). Indeed the ratio is closer to 3:5 (3:6 is 1:2 anyways). A better representation of the compound is SenS8-n.

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This compound is non polar because it is symmetrical in shape which makes the vector sum equal to zero. I think the electronegativity will not play any major role as opposite vectors are cancelling each other..

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  • $\begingroup$ This would be true if that were the actual structure of the compound. But it isn't. $\endgroup$ – matt_black Feb 22 at 12:57

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