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Lewis Dot Structure for H2S
Created by MakeTheBrainHappy.
This is the Lewis Dot Structure for H2S (hydrogen sulfide). The rules for drawing lewis structures permit the replacement of the bond lines with two electrons. As we have previously discussed, hydrogen only requires two electrons to fill up its valence shell because it only has a 1s shell as the very first element in the periodic table. Sulfur in this case shares the second required valence electron to fill hydrogen's octet. On the flip side, hydrogen shares its one electron which combined with sulfurs two lone pairs fill sulfur's valence shell with an octet.

Within the structure of the molecule it can be easily calculated that all of the formal structures are neutral based on the amount of electrons required to fill their valence electron. However in a similar manner as the H2O molecule, the presence of two lone pair electrons creates a dipole moment and similar "bent" structure. Although the resulting intermolecular forces are not considered hydrogen bonds due to the relatively lower electronegativity difference between hydrogen and sulfur than between hydrogen and oxygen, they still qualify this molecule with the designation of "polar."

H2S Gas by Concentration (Appearance)
H2S color at various concentrations. Source
Due to the weaker nature of these dipole interactions, H2S has a much lower melting point of -82˚C and boiling point of -60˚C. Nevertheless, H2S is extremely flammable and corrosive due to its polar nature.

H2S Probe
H2S probe. Source
In the absence of oxygen some bacteria are able to produce H2S as a byproduct of the decomposition of organic materials. H2S is considered a hazard to human health and therefore is monitored utilizing a probe as shown in the image above. H2S is most typically found at facilities producing crude oil or handling waste. It tends to accumulate in poor ventilated low lying spaces due to H2S having a molecular mass greater than that of the atmosphere. This increases the risk because higher levels of H2S damage the human body more than lower levels.

It smells like "rotten eggs" and can therefore be detected by humans.

Sulfur Cycle
The Sulfur Cycle. Source
Sulfur plays a key role in the "sulfur cycle" within earths atmosphere both in the process of decomposition by bacteria, within the material spewed from a volcano and from the products created by oil and natural gas manufacturing. Different kinds of bacteria either utilize H2S as a fuel source or release it into the environment as a byproduct of energy processing. Oftentimes H2S is lethal to many animals (not just humans) and in fact it has been implicated in numerous mass extinctions of life, most notably the Permian extinction event 252 million years ago.

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