Below 369 K alpha sulphur is stable and above this it transforms into beta sulphur. At 369K both the forms are stable.
The Allotropes of Sulphur
Sulphur exists in a variety of allotropes, the two most appropriate ones: of sulphur-yellow rhombic sulphur (α-sulphur) and the monoclinic (β-sulphur). The most intriguing characteristic is their thermal stability; the allotropes of sulphur are interconvertible, i.e. rhombic sulphur becomes monoclinic sulphur when heated above 369K.
- 369K is called transition temperature because both the allotropes of sulphur are stable at this temperature.
- In other words, we can conclude that α sulphur is stable below 369K and it becomes β-sulphur above that temperature.
- Rhombic and monoclinic sulphur, both have S8 molecules.
- The alternative packing of S8 molecules gives different crystal structures.