Problem 149 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following (a) Engel's sulphur (p) Crystalline formyellow crystals (b) \(\chi-\) sulphur (q) Fibrous or rubber like (c) Rhombic sulphur (r) Puckered \(\mathrm{S}_{\mathrm{g}}\) rings (crown configuration) (d) \(\gamma\)-monoclinic (s) \(\mathrm{S}_{4}\) rings, chair conformation, unstable

Step-by-Step Solution

Answer

(a) Engel's sulphur - (q); (b) χ-sulphur - (r); (c) Rhombic sulphur - (p); (d) γ-monoclinic - (s).

Step 1: Analyzing Engel's Sulphur

Engel's sulphur, also known as polymeric sulphur, is known for its fibrous or rubber-like texture. This type of sulphur is often stretched or pulled similar to a rubber band and matches description (q).

Step 2: Identifying χ-Sulphur

χ-Sulphur, or chi-sulphur, is characterized by puckered \( \mathrm{S}_8 \) rings, also known as the crown configuration. This matches description (r).

Step 3: Recognizing Rhombic Sulphur

Rhombic sulfur is the most stable and common form of crystals at room temperature. It forms yellow crystals that match description (p).

Step 4: Understanding γ-Monoclinic Sulphur

γ-Monoclinic sulphur has \( \mathrm{S}_4 \) rings in a chair conformation and is known to be unstable. It matches description (s).

Key Concepts

Crystalline Forms

Sulphur, a fascinating element, comes in various forms, most notably crystalline structures. Crystalline forms of sulphur have their atoms arranged in orderly and repeating patterns. This ordered arrangement gives rise to well-defined shapes, often in the form of yellow crystals.
These structures are vital for understanding the different physical properties sulphur exhibits. Notably, these forms can change based on temperature and conditions, transitioning from one allotrope to another, each having a unique internal structure.

• Crystalline sulphur typically refers to the organized lattice seen in these forms.
• Essentially, these forms include the stable rhombic sulphur and the slightly less stable monoclinic sulphur.

Understanding this concept helps explain why certain types of sulphur are more stable or reactive under varying environmental conditions.

Polymeric Sulphur

Polymeric sulphur, also known as Engel's sulphur, is quite distinct from its crystalline counterparts. This form is characterized by long chains of sulphur atoms. These fibres give it a fibrous or rubber-like texture, quite similar to elastic bands.
This unique property makes polymeric sulphur particularly interesting for industrial applications, where its elasticity can be a useful feature.

• Unlike the regular crystalline sulphur, polymeric forms are less ordered.
• This results in diverse physical properties like flexibility and tensile strength.

This form showcases the versatility and adaptability of sulphur as an element.

Rhombic Sulphur

Rhombic sulphur is the most stable and common crystalline form at room temperature. It forms beautiful yellow crystals, a characteristic feature that makes it easily recognizable.
This allotrope of sulphur is primarily found in nature and serves as the default sulphur form due to its stability.

• It persists up to temperatures of about 96°C.
• Beyond this temperature, it can transform into monoclinic sulphur.

Rhombic sulphur, due to its stability, is fundamental in the study of sulphur allotropes.

Monoclinic Sulphur

Monoclinic sulphur forms under conditions when rhombic sulphur is heated above 96°C but cooled below its melting point. It crystallizes with an elongated needle-like structure, which is less stable compared to rhombic sulphur.
Though not as stable, monoclinic sulphur is significant for its transitional role, often serving as a step on the way to other sulphur forms when changing temperatures.

• It exists in monoclinic crystal systems.
• Upon cooling, it reverts back to rhombic form.

Understanding monoclinic sulphur is crucial for comprehending sulphur's adaptability in different thermal conditions.

Puckered Rings

The concept of puckered rings in sulphur, specifically referring to \( \mathrm{S}_8 \) rings, describes a unique, non-planar structure. Known for their puckered or crown-like shape, these rings are pivotal in understanding the three-dimensional nature of sulphur molecules.
The bending and folding of these rings are what give sulphur its unique allotropes, like \( \chi-\) sulphur.

• Puckered rings provide insight into molecular flexibility.
• They contribute to sulphur's unique physical and chemical properties.

Recognizing this structure is essential in explaining why sulphur behaves unexpectedly in various reactions and conditions.

Sulphur Structures

Sulphur structures broadly refer to the different shapes and forms that sulphur atoms can arrange into. This includes everything from polymer chains to crystalline forms, each with distinct properties.
These diverse structures demonstrate sulphur's adaptability and its ability to form multiple allotropes.

• Different sulphur structures result in varying levels of stability and reactivity.
• They play key roles in industrial applications and scientific research.

By understanding these varied structures, one can better appreciate the role of sulphur in both natural and synthetic environments.