Sulphide is a chemical product generated when sulphur reacts with another element, usually a metal. It is frequently found in minerals such as pyrite (fool’s gold) and galena. Sulphides frequently emit unique odours (such as rotten eggs), and some are hazardous. They have a variety of purposes in industry, including mining for metals such as copper and lead. Sulphides also have a role in natural processes such as volcanic gas production and some biological activities.

This article deals with sulphides, their basic properties, formula, structure, reactions and commonly used sulphide compounds.

What are Sulphides?

Sulphide is a chemical product formed when sulphur reacts with another element preferably a metal. It is commonly found in minerals such as pyrite (fool’s gold) and galena (lead sulphide). Sulphides can have a variety of colours and fragrances. Some are bright and metallic, while others are matte and powdery. They are useful in industry for producing items like batteries and pigments, although some sulphides may emit unpleasant odours, such as the rotten egg odour of hydrogen sulphide gas.

Sulphide Ion

Sulhphide Ion is anion present in a sulhphide group of compound. For example, in Ferrous Sulphide(FeS), S is sulhphide ion

Sulphide Formula

Sulphide ions have the chemical formula (S²⁻). They have an oxidation state of -2. This structure allows sulphur to interact with other elements, producing sulphide compounds with molecular formulae such as XS, X2S, or XS2.

Valency of Sulphide

Valency of Sulphide is 2. Since, the electronic configuration of sulphur is 2, 8, 6. In its valence shell, there are six electrons. Thus sulphur requires two electrons to form sulphide. Hence, valency of sulfide is 2.

Sulphides Compounds

Some examples of sulphides include the following:

• Ferrous Sulphide: Its formula is FeS, also known as iron sulphide or pyrite. It is sometimes referred to as fool’s gold due to its dazzling look. Its melting point is 1195°C, and it is used to produce sulfuric acid.
• Zinc Sulphide: Its formula is ZnS, is used in luminous materials such as glow-in-the-dark paints and as a pigment in rubber, plastics, and textiles. Its melting point is about 1850°C.
• Copper (II) Sulphide: Its formula is Cu₂S and occurs naturally as chalcocite and is utilised in the manufacturing of copper metal. It melts at around 1030°C.
• Silver Sulphide: Its formula is AgS. It is often found in the mineral acanthite and is utilised in the manufacture of photographic film. The melting point is around 825°C.
• Tin sulphide(SnS₂): It is employed as a lubricant and in the manufacture of solar cells and sensors. Its melting point is about 882°C.
• Hydrogen Sulphide: Its formula is H₂S. Hydrogen sulphide smells like a rotten egg.

Chemical Properties of Sulphide

Chemical properties of sulphides are mentioned below:

• Sulphides of alkali and alkaline-earth metals are only slightly soluble in water and occur mostly in ionic form. Copper and zinc sulphides, on the other hand, are quite insoluble.
• While sulphides are normally innocuous, certain metal sulphides can produce poisonous hydrogen sulphide when exposed to strong acids.
• Organic sulphides are often highly flammable, producing sulphur dioxide (SO₂) upon combustion. Many organic sulphides have strong and disagreeable odours, including hydrogen sulphide and its salts.
• Free or aqueous sulphides are very corrosive to numerous metals, contributing to various types of corrosion.

Classes of Sulphides

Sulphides, a collection of sulfur-containing chemicals, are classified into three types: organic sulphides (also known as thioethers), inorganic sulphides, and phosphine sulphides. Let’s learn them in detail:

Inorganic Sulphides

These are salts derived from sulphur and a metal, such as iron sulphide or copper sulphide. Sulphur particles typically have a negative charge (S²⁻). Consider them to be sulphur compounds formed by combining metals.

Organic Sulphides

These sulphur atoms, also known as thioethers, are connected to two organic groups. They are present in organic molecules and can play a variety of functions in biological systems. Imagine sulphur creating a covalent connection with two carbon-based pals.

Phosphine Sulphides

These sulphides are generated when organic phosphines (phosphorus-containing compounds) combine with sulphur. In these compounds, sulphur is bound to phosphorus and possesses both ionic (charged) and covalent (shared) characteristics, similar to a giving and sharing relationship between sulphur and phosphorus.

Metal Derivatives of Sulphide

Metal sulphide derivatives create solid precipitates when sulphide sources such as NaHS, Na₂S, and H₂S react with transition metal cations in water. Inorganic sulphides are often poorly soluble in water. Cadmium yellow (CdS) is a well-known example, whereas silver sulphide (Ag₂S) appears as a black stain on sterling silver, which is commonly referred to as salts.

Transition metal sulphides have extremely covalent bonds, giving them semiconductor characteristics and a wide range of colours. They can be used as pigments, solar cells, and catalysts in a variety of chemical processes.

Sulphides include pyrite (iron disulphide), galena (lead sulphide), argentite (silver sulphide), cinnabar (mercury sulphide), realgar (arsenic sulphide), pentlandite (nickel sulphide), sphalerite (zinc sulphide), and chalcopyrite (iron-copper sulphide).

Preparation of Sulphide

Sulphides can be manufactured in a variety of ways, including:

Direct Combination: When iron (Fe) and sulphur (S) are combined, they react to produce iron sulphide (FeS), as illustrated in the equation:

Fe(s) + S(s) → FeS(s)

Reduction of sulphate: By lowering the quantity of sulphate, such as in the interaction between magnesium sulphate (MgSO4) and carbon (C), which produces magnesium sulphide (MgS) and carbon monoxide (CO) gas:

MgSO₄(s) + 4C(s) → MgS(s) + 4CO(g)

Precipitation of Insoluble Sulphides: Metal ions (M2+) combine with hydrogen sulphide gas (H2S) to generate metal sulphides (MS) and hydrogen ions (H+), as shown in the equation:

M²⁺ + H₂S(g) → MS(s) + 2H ⁺ (aq)

Structure of Sulphides

Sulphides have a wide range of structures, including molecular and polymeric bridges, and may be found in both nonmetals and metalloids.

Phosphorus has stable molecular chains of sulphides. Variants such as P₄S₄, P₄S₃, P₄S₇, P₄S₅, and P₄S₉ are derived from a tetrahedral P₄ molecular structure in which the initial P-P bonds are converted into P-S-P bonds. Notably, these phosphorus sulphides have low reactivity except with water, where they produce hydrogen sulphide (H₂S) and phosphoric acid (H₃PO₄), as seen in:

P₄S₁₀ + 16 H₂O = 10 H₂S + 4 H₃PO₄

Silicon disulfide, a metalloid, has a unique structure with numerous SiS4 polymer chains. Each chain is made up of tetrahedrons, with silicon atoms covalently bonding with sulphur atoms at each edge.

Chemical Reactions of Sulphide

Sulphide ions undergo significant chemical reactions and have unique properties:

Reaction of Sodium Sulphide with Water: In aqueous alkaline solutions of Na₂S, sulphide (S ²⁻) converts to hydrosulphide (SH⁻) following contact with water:

S ²⁻ + H₂O → SH ⁻ + OH ⁻

Reaction between Sulphides and Acids: The treatment of sulphide salts with acids generates hydrogen sulphide (H₂S):

S ²⁻ + H ⁺ → SH ⁻

SH ⁻ + H ⁺ → H₂S

Metal sulphides react with halogens to form sulphur and metal salts.

8 MgS + 8 I₂ → S₈ + 8 MgI₂

Oxidation of sulphide in the presence of an appropriate oxidizer generates sulfur:

16 HNO₃ + 24 H₂S → 16 NO + 3 S₈ + 32 H₂O

The oxidation of sulphide produces a variety of compounds depending on the reaction circumstances, including elemental sulphur, polythionates, sulphite, polysulphides, and sulphate.

Sulphide, Sulphite and Sulphate

Sulphide, Sulphite and Sulphate are three possible types of anion in chemical compounds formed with Sulphur. A basic understanding of these three types can be gained from the table below: