Red Sulphur

Sulfur forms several polyatomic molecules. The best-known allotrope is octasulfur, cyclo-S8. The point group of cyclo-S8 is D4d and its dipole moment is 0 D.

 Octasulfur is a soft, bright-yellow solid that is odorless.[a] It melts at 115.21 C (239.38 F),[b] and boils at 444.6 C (832.3 F).

 At 95.2 C (203.4 F), below its melting temperature, cyclo-octasulfur begins slowly changing from -octasulfur to the -polymorph.

The structure of the S8 ring is virtually unchanged by this phase transition, which affects the intermolecular interactions. Cooling molten sulfur freezes at 119.6 C (247.3 F), as it predominantly consists of the -S8 molecules. Between its melting and boiling temperatures, octasulfur changes its allotrope again, turning from -octasulfur to -sulfur, again accompanied by a lower density but increased viscosity due to the formation of polymers. At higher temperatures, the viscosity decreases as depolymerization occurs. Molten sulfur assumes a dark red color above 200 C (392 F). The density of sulfur is about 2 g/cm3, depending on the allotrope; all of the stable allotropes are excellent electrical insulators.

The sublimation of sulfur becomes noticeable more or less between 20 C (68 F) and 50 C (122 F), and occurs readily in boiling water at 100 C (212 F).

Sulfur is insoluble in water but soluble in carbon disulfide and, to a lesser extent, in other nonpolar organic solvents, such as benzene and toluene.