Allotropes of Sulfur
Allotropes are different structural modifications of the same element. Sulfur has two important allotropic forms; they are crystalline sulfur and amorphous or noncrystalline sulfur.
Important crystalline forms of sulfur are rhombic or octahedral sulfur and monoclinic or prismatic Sulfur.
Crystalline sulfur consists of eight sulfur atoms arranged in a puckered-ring structure. These can be packed together in two different forms rhombic crystals and needle-shaped monoclinic crystals.
Stable allotropes are excellent electrical insulators.
Noncrystalline sulfur also known as plastic sulfur as it looks like elastic meterial.
Characteristics and differences of allotropic forms of Sulfur:
| Allotropes of Sulfur | |||
|---|---|---|---|
| Allotropic Forms | |||
| Characteristics | Rhombic | Monoclinic | Amorphous/Plastic |
| Shape | Rhombic or Octahedral crystals | Needle-shaped monoclinic or Prismatic crystals | Noncrystalline |
| Color | Pale yellow, opaque, brittle | Yellow, waxy, transparent, brittle | Dark, elastic, plastic |
| Stability | It is stable crystalline form at ordinary temprature 269 K. | It is stable between 269 K and 392 K. | Unstable |
| Preparation | It is prepared by slow evaporation of solution of sulfur in carbon disulphide CS2. | Crystals formed from molten Sufur as it cools. | When molten sulphur is heated up to boiling and then cooled quickly, it turns into elastic meterial which is called plastic sulphur. |
| Solubility | Soluble in most organic solvents. | Soluble in most organic solvents. | Insoluble in most organic solvents. |