Give a detailed account on allotropes of sulphur.

Explanation

(a) Rhombic Sulphur (`alpha` - Sulphur):
(a) It is yellow in colour.
(b) Its melting point is 385.8K and specific gravity is 2.06.
(c) It is stable form of sulphur at room temperature.
(d) It is formed on evaporating the solution of sulphur in `CS_(2)`.
(e) It in insoluble in water, readily soluble in `CS_(2)` and dissolves to some extent in benzene, alcohol and ether.
(b) Monoclinic Sulphur ( `beta`- Sulphur):
(a) Its melting point is 393K and specific gravity is 1.98.
(b) It is prepared by melting rhombic sulphur in a dish and cooling , till crust is formed. Two holes are made in crust and remaining liquid is powered out. On removing crust, colourless needle- shaped crystals of `beta`- sulphur is formed. (c) Moniclinic sulphur is stable above 369K and below 369K `alpha` - sulphur is stable.
(d) At 369K both forms are stable and this temperature is called transition temperature.
(e) Both rhombic and monoclinic sulphur have `S_(8)` molecules, these are packed to give different crystal structure `S_(8)` form is puckered and has crown shape.
Several other modifications containing 6-20 sulphur atoms per ring are synthesised.

(f) In cyclor-`S_(6)` the ring adopts chair form.

(g) At elevated temperatures (`~1000K`), `S_(2)` is dominant species and is paramagnetic like `O_(2)`.