Question

We humans have known elemental Sulphur from the earliest times. In the last two decades, the allotropy of sulfur has been explored in great detail. The most common naturally occurring allotrope,$S_8$ cyclo-octasulphur, has a puckered three dimensional “crown” like arrangement of atoms around the ring. This homocyclic allotrope forms “needle-like” crystals above ${95}^{\circ }$ C, but below that temperature, crystallizes in a “chunky” fashion. The crystals, which are referred to as monoclinic and rhombic forms, differ simply in the way in which the molecules pack. These are allotropes of each other – True or False?

• A. True
• B. False

Answer 1

The correct option is B False

The question looks long for a true or false type doesn’t it. Shall we keep the answer very short – yes?
Polymorphs are defined as different crystal forms in which identical units of the same compound are packed differently. Strictly speaking, the three varieties of cyclo-octasulphur – the $\alpha$ -Sulphur, $\beta$ -Sulphur and the $\gamma$ -Sulphur are all polymorphs and not allotropes. Allotropes contain different molecular units!

The repeating molecular unit of cyclo-octasulphur – the $S_8$ molecule looks like: