Chemistry · Ch 7 — Elements of Groups 16, 17 and 18

Allotropes of sulfur

7.7.1

Allotropes of sulfur

Sulfur exhibits numerous allotropic forms. However, rhombic sulfur ( $\alpha$ -sulfur) and monoclinic sulfur ( $\beta$ -sulfur) are the most important allotropes of sulfur. Table 7.7 compares them property by property.

Table 7.7 Allotropes of sulfur

	Rhombic Sulfur ( $\alpha$ - Sulfur)	Monoclinic Sulfur ( $\beta$ - Sulfur)
Color	Pale Yellow	Bright yellow solid
Shape	Orthorhombic crystals	Needle shaped monoclinic crystals
M. P.	385.8 K	393 K
Density	2.069 g/cm³	1.989 g/cm³
Solubility	Insoluble in water and soluble in $\mathrm{CS_2}$	Soluble in $\mathrm{CS_2}$
Stability	Stable below 369 K and transforms to $\beta$ -sulphur above this temperature.	Stable above 369 K and transforms into $\alpha$ -sulphur below this temperature.
Structure	$\mathrm{S_8}$ molecules having puckered ring structure	$\mathrm{S_8}$ molecules with puckered ring structure
Method of preparation	It is prepared by evaporation of roll sulphur in $\mathrm{CS_2}$ .	Rhombic sulphur melted in a dish and cooled till a crust is formed. Two holes are made in the crust and the remaining liquid is poured out, to give needle shaped crystals of $\beta$ -sulphur.

(The book's own density cells print "2.069/ cm³" and "1.989 / cm³" — the unit intended, and restored above, is g/cm³.) …

Figure 7.7.1aThe puckered crown-shaped eight-membered S8 ring of rhombic sulfur, drawn as the textbook's flat zig-zag projection of eight circled sulfur atoms, with the printed S-S bond length and the 107 degree ring angle marked.

Fig. 7.7.1a — The puckered crown-shaped eight-membered S8 ring of rhombic sulfur, drawn as the textbook's flat zig-zag projection of eight circled sulfur atoms, with the printed S-S bond length and the 107 degree ring angle marked.

Drawn by us to help you understand the concept clearly, and verified to make sure it's accurate. For exams, practice from your textbook's own diagram.

What this drawing shows (printed inside the "Remember..." box, captioned "Structure of S₈ ring in rhombic sulfur"). The eight S atoms of the $\mathrm{S_8}$ molecule form a puckered, crown-shaped ring - the flat zig-zag you see here is the book's projection of that crown, with alternate atoms raised and lowered. The dashed guide marks the ring angle of 107°. *(The book's bond-length label prints "2.04 pm" - its own slip of the units: the S-S bond …

Figure 7.7.1bThe chair conformation of the six-membered cyclo-S6 sulfur ring, drawn with six circled sulfur atoms, with its bond length of about 205.7 pm and ring angle of about 102.2 degrees marked.

Fig. 7.7.1b — The chair conformation of the six-membered cyclo-S6 sulfur ring, drawn with six circled sulfur atoms, with its bond length of about 205.7 pm and ring angle of about 102.2 degrees marked.

Drawn by us to help you understand the concept clearly, and verified to make sure it's accurate. For exams, practice from your textbook's own diagram.

What this drawing shows (printed inside the "Remember..." box, captioned "Chair form of S₆"). In cyclo- $\mathrm{S_6}$ the six-membered ring adopts the chair form, just as the box's text says. The guides mark the S-S bond length (205.7 pm) and the ring angle (102.2°). *(In the book these two values print garbled - as "205.7°c" and "0 …

Start your 14-day free trial to unlock the full solution →

← Previous · 7.7Q2 — What is the difference between allotropy and polymorphism ?Next · 7.7.1 →Problem 7.7 — Which form of sulfur shows paramagnetic behaviour ?