Triplet oxygen
Triplet oxygen, 3O2, refers to the S = 1 electronic ground state of molecular oxygen (dioxygen). Molecules of triplet oxygen contain two unpaired electrons, making triplet oxygen an unusual example of a stable and commonly encountered diradical: it is more stable as a triplet than a singlet. According to molecular orbital theory, the electron configuration of triplet oxygen has two electrons occupying two π molecular orbitals (MOs) of equal energy (that is, degenerate MOs). In accordance with Hund's rules, they remain unpaired and spin-parallel, which accounts for the paramagnetism of molecular oxygen. These half-filled orbitals are antibonding in character, reducing the overall bond order of the molecule to 2 from the maximum value of 3 that would occur when these antibonding orbitals remain fully unoccupied, as in dinitrogen. The molecular term symbol for triplet oxygen is 3Σ−
g.
| Names | |
|---|---|
| IUPAC name
Triplet oxygen | |
| Systematic IUPAC name
Dioxidanediyl (substitutive) dioxygen(2•)(triplet) (additive) | |
| Identifiers | |
3D model (JSmol) |
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| ChEBI | |
| ChemSpider | |
| EC Number |
|
| 492 | |
| KEGG | |
| MeSH | Oxygen |
PubChem CID |
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| RTECS number |
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| UNII | |
| UN number | 1072 |
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| Properties | |
| O2 | |
| Molar mass | 31.998 g·mol−1 |
| Appearance | Colorless gas |
| Melting point | −218.2 °C; −360.7 °F; 55.0 K |
| Boiling point | −183.2 °C; −297.7 °F; 90.0 K |
| Structure | |
| Linear | |
| 0 D | |
| Thermochemistry | |
Std molar entropy (S⦵298) |
205.152 J K−1 mol−1 |
Std enthalpy of formation (ΔfH⦵298) |
0 kJ mol−1 |
| Pharmacology | |
| V03AN01 (WHO) | |
| Hazards | |
| GHS labelling: | |
| Danger | |
| H270 | |
| P220, P244, P370+P376, P403 | |
| NFPA 704 (fire diamond) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references | |