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?

True

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False

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Solution

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 $α$ -Sulphur, $β$ -Sulphur and the $γ$ -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:

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An element E exists in three allotropic forms A, B and C. In allotrope A, the atoms of element E are joined to form spherical molecules. In allotrope B, each atom of element E is surrounded by three other E atoms to form a sheet-like structure. In allotrope C, each atom of element E is surrounded by four other E atoms to form a rigid structure.
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(b) What is allotrope A?
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(d) What is allotrope C?
(e) Which allotrope is used in making jewellery?
(f) Which allotrope is used in making the anode of a dry cell?

Q. The phenomenon of the existence of a chemical element in two or more forms differ in physical properties but of the same chemical nature is known as Allotropy. Carbon has two major allotropes diamond and graphite and the third one is Buckminsterfullerene. Diamond has a three-dimensional network of covalent bonds and is hard. In graphite, the carbon atoms are arranged in flat parallel layers as regular hexagons resulting in soft and ________ nature.

Q. Which of the following options regarding sulphur is correct?

(a) Density of monoclinic sulphur is more than rhombic sulphur due to the arrangement of puckered rings.
(b) In a puckered ring one sulphur is bonded with 2 other sulphur atoms.
(c) The melting point of rhombic sulphur is considered as transition temperature of sulphur.
(d) Flower of sulphur is the vapour form of sulphur.

Q. From the two allotropes of sulphur, Rhombic sulphur and Monoclinic sulphur, which is more stable?

Q. ASSERTION:

Δ_{f} H^{o}

for white phosphorus has been taken to be zero, whereas black phosphorus is the most stable allotrope of phosphorus and this is the only exception.

REASON:
The reference standard state of white phosphorus is taken despite the fact that this form is not the most stable allotrope but simply the most reproducible form of phosphorus.

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