It is called ρ-sulfur, ε-sulfur, Engel's sulfur and Aten's sulfur. Cyclo-S 6 is orange-red and forms a rhombohedral crystal. Engel in 1891 by reacting concentrated HCl with thiosulfate, HS 2O 3 −. This has not been isolated, but has been detected in molten sulfur. Solid cyclo-sulfur allotropes cyclo-S 5, pentasulfur The latest view, based on theoretical calculations is that it has a ring structure. Various forms, (e.g chains, branched chains and rings) have been proposed. This has been detected in the vapour phase but has not been fully characterised. Its structure is bent, similar to ozone, O 3. S 3 is found in sulfur vapour, comprising 10% of vapour species at 440☌ and 10mm Hg. The blue colour of burning sulfur is due to emission of light by the S 2 molecule produced in the flame. It is a singlet diradical like dioxygen with an S-S bond length of 188.7 pm. at low pressure (1mm Hg) at 530☌ it comprises 99% of vapour species. S 2 is the predominant species in sulfur vapour above 720☌. Ĥ high pressure phases (at ambient temperature) including two that are metallic and become superconducting at low temperature and some additional phases photo-induced below 20-30GPa. ĭark coloured liquid that develops as λ-sulfur is left molten. The dark coloured viscous liquid formed when π-sulfur is heated and the solid when cooled. Light yellow mobile liquid formed when β-sulfur first melts at 119.6☌. Sometimes called polymeric sulfur, μ-S or ω-S.Ī mixture of allotropic ψ-sulfur and cyclo forms mainly γ-cycloS 8Ī mixture of chains with a minimum of soluble species. Quenched liquid sulfur with soluble species extracted with CS 2. Consists of a mixture of catena sulfur and cyclo sulfur. Quenched molten sulfur plastic sulfur at first crystallises to amorphous or glassy sulfur. Contains contains helical chains partially crossed. Generally synthesised rather than obtained by treatment of another form of elemental sulfur. Pure forms all allotropes, cyclo-S 9 has four forms, cyclo-S 18 has two forms. Found in nature as the rare mineral rosickyiteĬyclo-(nona deca undeca dodeca trideca tetradeca pentadeca octadeca eicosa)sulfur Light yellow solid, crystal monoclinic, consisting of S 8 puckered rings. Γ-sulfur "nacreous sulfur" "mother of pearl sulfur" "Gernez’s sulfur" or "Muthmann's sulfur III". Only stable above 95☌, it reverts to α-sulfur at room temperature. Yellow solid, consisting of S 8 puckered rings. Β-sulfur "monoclinic sulfur" "prismatic sulfur" "Muthmann's sulfur II" The thermodynamically stable form at ordinary temperatures Yellow solid consisting of S 8 puckered rings. Α-sulfur "orthorhombic sulfur" "rhombic sulfur", "flowers of sulfur", "roll sulfur" "milk of sulfur", "Muthmann's sulfur I" Not yet isolated only detected in sulfur melts.Ĭyclo-hexasulfur, ρ-sulfur "ε-sulfur", "Engel's" sulfur, "Aten's sulfur"įirst synthesised in 1891, the ring adopts a chair form in the solid.Īn usual mixed crystal with alternating layers of cyclo-S 6 and cyclo-S 10įour forms known, two(γ-, δ- ) characterised. Structure not determined but calculations indicate it to be cyclo-S 4 This system predates the discovery of new forms that have been synthesised rather than prepared from elemental sulfur.Ī diatomic gas with a triplet ground state like dioxygen.Ī cherry red triatomic gas with a bent ozone like structure. A commonly used naming system uses Greek suffixes (α, β) etc. "Muthmann's sulfur I" or "Engel's sulfur". "mother of pearl sulfur", or alternatively named for a chemist who was pre-eminent in identifying them e.g. Some forms have been named for their appearance e.g. pure forms, whilst others have proved to be mixtures. The range of molecular allotropes possessed by sulfur can in part be ascribed to the wide range of bond lengths (180pm -260pm) and inter bond angles(90° - 120°) exhibited by the S-S bond and its strength, (the unrestrained S-S single bond has a high bond energy of 265 kJmol -1 ).Įarly workers identified some forms that have later proved to be allotropes i.e. There are also gases, S 2, S 3, S 4 and S 5 and perhaps five or more high pressure forms, two of which are metallic. In addition to these there are other solid forms that contain sulfur rings of 6, 7, 9-15, 18 and 20 atoms. Chemistry students may have seen "plastic sulfur", this is not an allotrope but is a mixture that contains long chain polymeric sulfur, two forms of which have been identified as allotropes. The most common form found in nature is yellow orthorhombic α-sulfur, which contains puckered rings of S 8. Sulfur is second only to carbon in this respect. There are a number of allotropes of sulfur.
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