What is the Difference Between Rhombic and Monoclinic Sulphur?

Rhombic and monoclinic sulfur are two allotropic forms of sulfur, which are distinguished by their crystal structures, colors, densities, and stabilities at different temperatures. Here are the main differences between them:

1. Crystal Structure: Rhombic sulfur (α-sulfur) forms orthorhombic crystals, while monoclinic sulfur (β-sulfur) forms needle-shaped monoclinic crystals.
2. Color: Rhombic sulfur is a pale yellow-colored solid, whereas monoclinic sulfur is a bright yellow solid.
3. Density: Rhombic sulfur has a density of 2.06 g/cm³, while monoclinic sulfur has a density of 1.98 g/cm³.
4. Melting Point: Rhombic sulfur has a melting point of 385.8 K, while monoclinic sulfur has a melting point of 393 K.
5. Stability: Rhombic sulfur is stable below 369 K and transforms to β-sulfur above this temperature. Monoclinic sulfur is stable above 369 K and transforms into α-sulfur below this temperature. It is only stable at temperatures between 96°C and 119°C.
6. Preparation: Rhombic sulfur is prepared by the evaporation of roll sulfur in CS2, while monoclinic sulfur is prepared from rhombic sulfur by melting it in a dish and cooling until a crust is formed.

In summary, rhombic and monoclinic sulfur differ in their crystal structures, colors, densities, melting points, stabilities, and methods of preparation.

Comparative Table: Rhombic vs Monoclinic Sulphur

The main difference between rhombic and monoclinic sulphur lies in their crystal structure, color, and stability at different temperatures. Here is a table comparing the two allotropes:

Rhombic sulphur is a pale yellow solid with needle-like crystals, whereas monoclinic sulphur is a bright yellow solid with orthorhombic crystals. Rhombic sulphur transforms into monoclinic sulphur at temperatures above 369 K.