Ozone

Names IUPAC nameSystematic IUPAC nameOther names Identifiers ChEBIChemSpiderECHA InfoCard100.030.051EC Number1101 MeSHOzoneRTECS numberUNIIProperties O₃Molar mass47.997 g·mol Appearance Colourless to pale blue gas OdorPungent, metallic, dry Density2.144 g/L (at 0 °C) Melting point−192.2 °C; −313.9 °F; 81.0 K Boiling point−112 °C; −170 °F; 161 K 1.05 g L (at 0 °C) Solubility in other solvents Very soluble in CCl₄, sulphuric acid, Slightly soluble in water. Vapor pressure55.7 atm (−12.15 °C or 10.13 °F or 261.00 K) Conjugate acidProtonated ozone+6.7·10 cm/mol 1.2226 (liquid), 1.00052 (gas, STP, 546 nm—note high dispersion) Structure C_2vDigonal Dihedral Hybridisationsp for O1 0.53 D Thermochemistry 238.92 J K mol 142.67 kJ mol Hazards GHS labelling: DangerH270, H314, H330, H335, H341, H361, H370, H410P203, P220, P244, P260, P264+P265, P270, P271, P273, P280, P284, P301+P330+P331, P302+P361+P354, P304+P340, P305+P351+P338, P308+P316, P362+P364, P370+P376, P391, P403+P233, P405NFPA 704 (fire diamond) Lethal dose or concentration (LD, LC): 12.6 ppm (mouse, 3 hr)
50 ppm (human, 30 min)
36 ppm (rabbit, 3 hr)
21 ppm (mouse, 3 hr)
21.8 ppm (rat, 3 hr)
24.8 ppm (guinea pig, 3 hr)
4.8 ppm (rat, 4 hr) NIOSH (US health exposure limits): TWA 0.1 ppm (0.2 mg/m) C 0.1 ppm (0.2 mg/m) 5 ppm Related compounds Sulphur dioxide
Trisulphur
Disulphur monoxide
Cyclic ozone

Ozone (), also called trioxygen, is an inorganicmolecule with the chemical formulaO
₃. It is a pale-blue gas with a distinctively pungent odour. It is an allotrope of oxygen that is much less stable than the diatomic allotrope O
₂, breaking down in the lower atmosphere to O
₂ (dioxygen). Ozone is formed from dioxygen by the action of ultraviolet (UV) light and electrical discharges within the Earth's atmosphere. It is present in very low concentrations throughout the atmosphere, with its highest concentration high in the ozone layer of the stratosphere, which absorbs most of the Sun's ultraviolet (UV) radiation.

Ozone's odour is reminiscent of chlorine, and detectable by many people at concentrations of as little as 0.1 ppm in air. Ozone's O₃structure was determined in 1865. The molecule was later proven to have a bent structure and to be weakly diamagnetic. At standard temperature and pressure, ozone is a pale blue gas that condenses at cryogenic temperatures to a dark blue liquid and finally a violet-black solid. Ozone's instability with regard to more common dioxygen is such that both concentrated gas and liquid ozone may decompose explosively at elevated temperatures, physical shock, or fast warming to the boiling point. It is therefore used commercially only in low concentrations.

Ozone is a powerful oxidising agent (far more so than dioxygen) and has many industrial and consumer applications related to oxidation. This same high oxidising potential, however, causes ozone to damage mucous and respiratory tissues in animals, and also tissues in plants, above concentrations of about 0.1 ppm. While this makes ozone a potent respiratory hazard and pollutant near ground level, a higher concentration in the ozone layer (from two to eight ppm) is beneficial, preventing damaging UV light from reaching the Earth's surface.