Structure of Sulphides

Sulphides exist in nature both as a negative ion as well as in the form of compounds that carry a negative charge. These compounds are built of multiple S2- ions. In inorganic chemistry, we also come across sulphides as a separate class of compounds, for example, silicon disulfide and lead sulphide. From sulphides, both bisulfite and hydrogen sulphide (H2S) can be derived as conjugate acids. The sulphide anions are located in a variety of minerals that occur naturally. Some common sources include galena, cinnabar, molybdenite, and chalcopyrite. sulphides when dissolved in water can cause severe harm to humans in the form of corrosion. This includes the sulfuric acid and bisulfite (HS–) solutions that damage steel and copper fixtures. This common phenomenon is scientifically defined as sulphide stress cracking of stainless steel. 

Structure of sulphides

sulphides are structured in some nonmetals and metalloids both in molecular form as well as polymeric bridges. For instance, in phosphorus, we notice a stable chain of sulphides in molecular form. The molecular sulphide exists in the form of P4S4, P4S3, P4S7, P4S5, and P4S9 in Phosphorus. These sulphide molecules descend from a P4 tetrahedral molecular structure. The original P – P links in all the above-mentioned structures are altered by the subsequent P – S – P bonds.

 However, these phosphorus sulphides do not readily react when they are present in CS2 or Carbon disulfide. The only exception is water.

Here is the balanced chemical reaction: P4S10 + 16 H2O = 10 H2S (hydrogen sulphide) + 4 H3PO4 (phosphoric acid).

Let us take another example of sulphide present in the metalloid silicon. In silicon disulfide, we notice a typical structure that depicts multiple polymers of SiS4. These tetrahedrons are made up of a silicon atom which is covalently bonded to sulphur atoms at the four edges.

The formula of Sulphate

Atmospheric conditions on earth are favourable for generating the natural abundance of sulphate in minerals that are distributed all over the world. The formula of sulphate is SO42-. We have just learned about the mineral rocks that are composed of sulphides as one of their key ingredients. These rocks along with the volcanic deposits are counted as the major sources of sulphates. It is crucial to assimilate the chemical bonding besides knowing the formula of sulphate. The formula SO42- clarifies the fact that each ion is composed of oxygen and sulphur atomic particles. Four constituent oxygen atoms enclose the central sulphur particle to form a symmetrical plane. The formula of sulphate carries a -2 charge which is the resultant effect of the constituent oxygen atoms that tend to remain in a negative state as two oxygen atoms only get to form a single bond with the central atom. The bonds are depicted at an angle of 109.5 degrees as per the VSEPR model. However, we simply represent the structure as:

O

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O— —   S   —  O—

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O

The functional groups of sulphides

The chemical bonding of C – S – C is generally referred to as sulphides in the realm of organic chemistry. Chemists represent sulphides with an empirical formula C6H4S. In the following few points let us discuss the most common sets of compounds that are identified as the functional groups of sulphides.

• Sulfenic acid is a common oxoacid that is represented with the formula RSOH. These sulfuric acids are not stable in pure form. A very popular example of this type of oxoacid is benzene sulfonic acid.

• Another class of acids depicts the linkage as H – S = (O2) – OH. Chemists identify this sulfonic acid as a tautomer of H2O3.

• Sulfoxide is another functional group of sulphides that incorporate two central carbon atoms. Allin is a natural source of sulfoxide in nature.

• Sulfone is identified easily owing to its central sulphur particle that shares a double linkage with the constituent oxygen atoms. Sulfones produce sulfoxides when they are processed from their precursors, i.e., the sulphides. It is refrained from being called a sulphone as per the latest guidelines published by the IUPAC. 

Examples of sulphides

We witness the existence of three categories of sulphides in nature. The first class is called organic sulphides which are produced due to covalent bonding between a sulphur atomic particle and a couple of organic groups. These are commonly known as thioethers. Methyl phenyl sulphide or C6H5SCH3 is an example of organic sulphide.

The second category or phosphine sulphides exhibits both electrovalent and covalent linkage between the phosphorus and sulphur atoms. Triphenylphosphine sulphide is an example of phosphine sulphide. Its formula is given as (C6H5)3PS.

 Lastly, we come across the inorganic sulphides or salts that comprise S2- anion. Hydrogen sulphide (H2S) and Carbon disulfide (CS2) are two examples of inorganic sulphides.

Conclusion

In chemistry, the word ‘sulphides’ refers to a group of chemical substances that contain sulphur as their central atom. Some of these substances are found naturally while many are unstable and are produced to fulfil certain purposes of man.