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

Question

Match the following Column-I (Allotropic form) (a) Engel's sulphur (b) \(\chi-\) sulphur (c) Rhombic sulphur (d) \(\gamma\)-monoclinic | Column-II (Structure) | | :--- | | (p) Crystalline form- | | yellow crystals | | (q) Fibrous or rubber like | | (r) Puckered S_(8) rings | | (crown configuration) | | (s) S_(4) rings, chair | | conformation, | | unstable |

Step-by-Step Solution

Answer

(a)-(q), (b)-(s), (c)-(r), (d)-(p)

Step 1: Understanding the Problem

First, we need to understand that the exercise involves matching forms of sulphur with their respective structural descriptions. The goal is to correctly associate each allotropic form from Column-I with a description from Column-II.

Step 2: Match Engel's sulphur

Engel's sulphur (a) is known for having an unusual fibrous or rubber-like structure. Thus, it matches with description (q) in Column-II.

Step 3: Match χ-sulphur

χ-sulphur (b) is characterized by having S₄ rings in a chair conformation and is unstable. Therefore, it corresponds to description (s).

Step 4: Match Rhombic sulphur

Rhombic sulphur (c) is the most stable form at room temperature and is known for its crystalline form with puckered S₈ rings in a crown configuration. Thus, it matches with (r).

Step 5: Match γ-monoclinic

γ-monoclinic (d) forms yellow crystals when cooled slowly from the melt, indicating its match with (p).

Key Concepts

Engel's sulphur

Engel's sulphur is a fascinating allotropic form due to its unique structure. Unlike more common sulphur forms, Engel's sulphur exhibits a fibrous or rubber-like appearance. This makes it stand out compared to the typical crystalline forms we're used to seeing with sulphur. The structure of Engel’s sulphur owes itself to its unusual bonding arrangement. Instead of forming standard crystal lattices, it creates a more flexible and less rigid formation. This interesting property allows Engel's sulphur to be studied for its potential uses in various flexible and pliable materials. Such unique physical traits invite further exploration into the applications that this form might have in practical contexts, such as elastic materials or novel chemical substances.

χ-sulphur

The allotropic form known as χ-sulphur is quite distinctive in its structure. It includes S₄ rings that adopt a chair conformation, reminiscent of the shape seen in cyclobutane structures. However, unlike more stable sulphur allotropes, χ-sulphur remains unstable. This instability is attributed to the tension within the S₄ ring structure, which is at odds with the preferred eight-membered ring of other sulphur forms like the S₈ rings. The understanding of χ-sulphur's structural peculiarities allows chemists and material scientists to study its properties under controlled conditions to see how it might be stabilized or used. Due to its instability, χ-sulphur tends to revert quickly to more stable forms unless measures are taken to maintain its structure. Studying it can provide insights into sulphur chemistry and potential applications in creating novel compounds through clever chemistry tricks.

Rhombic sulphur

Rhombic sulphur is perhaps the most commonly referenced form of sulphur and is often considered the most stable at room temperature. It forms a crystalline structure characterized by puckered S₈ rings arranged in a crown configuration. This structure is beneficial because it leads to the stability and resilience that define rhombic sulphur. It is the default manifestation of sulphur under regular conditions, outlasting other forms due to its energetic favorability. The crystalline nature of rhombic sulphur not only influences its physical properties, making it a standard reference for pure elemental sulphur, but also plays a crucial role in industrial applications where stability and reliability are essential. From fireworks to fungicides, rhombic sulphur finds its utility across diverse sectors due to its stable nature.

γ-monoclinic sulphur

γ-monoclinic sulphur is another intriguing structural variant of sulphur. It forms bright yellow crystals, particularly when the liquid sulphur is cooled slowly. This contrasts with the orthorhombic rhombic sulphur form. The transition from rhombic to γ-monoclinic occurs at higher temperatures, approximately around 96°C, and these yellow crystals can revert if conditions change. This form displays certain characteristic angles and planes in the crystal structure, leading to interesting material properties useful in scientific investigations. Understanding γ-monoclinic sulphur is critical because it offers insights into sulphur's adaptability and the phase transitions it undergoes. This knowledge can be employed in refining processes, creating stable compounds under specific conditions, and even in theoretical models predicting the behavior of sulphur under varied environmental and industrial scenarios.

Chemical Structures

Chemical structures are vital to understanding how substances like sulphur exhibit various properties and behaviours. The arrangement of atoms in a molecule or allotrope determines everything from its phase to its reactivity, color, and stability. In sulphur, the formation of S₈ rings as seen in rhombic sulphur is a key example. These rings demonstrate the typical puckered shape essential to the substance's stability. Each atom is bonded to two others, forming a closed cyclic structure that gives sulphur its characteristic properties, including smell and taste. Understanding these structures is not only important for theoretical chemistry but also immensely practical.

• Applications in industries such as rubber manufacturing and fertilizers.
• Uses in creating breakthroughs in synthetic chemistry.

Chemical structure analysis aids scientists in designing new materials or improving existing ones by better understanding atomic interactions at the molecular level.