| Disulfur | |
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Disulfur |
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Other names
Diatomic sulfur Sulfur |
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| Identifiers | |
| CAS number | 23550-45-0 |
| PubChem | 5460602 |
| ChemSpider | 4574100 |
| ChEBI | CHEBI:29387 |
| Gmelin Reference | 753 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | S2 |
| Molar mass | 64.13 g mol−1 |
| Exact mass | 63.944141380 g mol-1 |
| Dipole moment | 0 D |
| Thermochemistry | |
| Std enthalpy of formation ΔfH |
128.60 kJ mol-1 |
| Standard molar entropy S |
228.17 kJ K-1 mol-1 |
| Specific heat capacity, C | 32.51 kJ K-1 mol-1 |
| Related compounds | |
| Related compounds | Triplet oxygen |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Disulfur is the diatomic molecule with the formula S2.[1] It is analogous to the dioxygen molecule but rarely occurs at room temperature. This violet gas is commonly generated by heating sulfur above 720 °C and comprises 99% of vapor species at low pressure (1 mm Hg) at 530 °C. S2 is one of minor components of the atmosphere of Io’s, which is dominantly composed of SO2.[2] Diatomic molecules are common containing C, O, N and F, but for heavier elements they are often only stable at high temperatures.
Disulfur results when an atmosphere of COS is irradiated with UV light using a mercury photosensitizer or when CS2, H2S2, S2Cl2 or C2H4S are photolyzed. Singlet S2 is also formed when sulfur compounds such as H2S, PSF3 or COS are photolyzed. S2 can be generated by heating various organosulfur precursors.[3]
S2 exists in the triplet state like O2, i.e. both are diradicals. It has S-S double bond length of 189 pm, much shorter than the S-S single bonds in S8, which are 206 pm. In its Raman spectrum, the S-S vibrational band is observed at 715 cm−1.[4] The corresponding vibrational band of O-O is found at 1122 cm−1. The S-S bond energy is 265 kJ/mol compared to 498 kJ/mol for O2.
Sulfur has a large number of allotropes, perhaps as many as thirty. Their specific properties are distinguishable by various types of spectroscopy. The only stable form of sulfur at normal condition is S8.[5]