Ozone

Ozone
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IUPAC name	Trioxygen
Other names	2λ4-trioxidiene; catena-trioxygen
Identifiers
CAS number	10028-15-6
PubChem	24823
EC number	233–069–2
MeSH	Ozone
ChEBI	CHEBI:25812
RTECS number	RS8225000
SMILES	[O-][O+]=O
	InChI
Gmelin Reference	1101
Properties
Molecular formula	O3
Molar mass	47.98 g mol-1
Appearance	Colourless to pale blue gas<
Odor	Pungent
Density	2.144 mg cm−3 (at 0 °C)
Melting point	-192 °C, 81 K, -314 °F
Boiling point
Solubility in water	1.05 g L−1 (at 0 °C)
Solubility in other solvents	Very soluble in CCl4, sulfuric acid
Vapor pressure	55.7 atm (−12.15 °C or 10.13 °F; 261.00 K)
Magnetic susceptibility (χ)	+6.7·10−6 cm3/mol
Refractive index (nD)	1.2226 (liquid), 1.00052 (gas, STP, 546 nm — note high dispersion)
Structure
Space group	C2v
Coordination; geometry	Digonal
Molecular shape	Dihedral
Hybridisation	sp2 for O1
Dipole moment	0.53 D
Thermochemistry
Std enthalpy of; formation ΔfHo298	142.67 kJ mol−1
Standard molar; entropy So298	238.92 J K−1 mol−1
Hazards
NFPA 704	0 4 4
U.S. Permissible; exposure limit (PEL)	TWA 0.1 ppm (0.2 mg/m3)
	Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Ozone, or trioxygen, is a chemical with the symbol O₃. This means one molecule of ozone is made of three oxygen atoms. Ozone is rarely called trioxygen, even though this is its IUPAC systematic name.^[3] Ozone is formed from oxygen gas (O₂) by the action of ultraviolet light and also atmospheric electrical discharges. It is present in low concentrations throughout the Earth's atmosphere. In total, ozone makes up only 0.6 ppm (parts per million) of the atmosphere by volume.

Christian Friedrich Schönbein

Ozone is important to life on planet Earth. There is a portion of the stratosphere with a high concentration of ozone, called the ozone layer. The ozone layer is 10 to 50 kilometers above the ground. It filters out damaging ultraviolet radiation from the Sun,^[4] like a kind of sun screen. Without this ozone layer things would not have been able to live on the surface of our planet. The ozone layer also absorbs a lot of heat from the sun's rays.

However, ozone is toxic to animals and plants above concentrations of about 0.1 ppm. In humans, it can cause nasal and throat irritation, and nausea.^[5] Extended exposure can cause lung oedema.^[5] 0.100 ppm is the maximum allowable limit for industrial, public, or occupied spaces in England, Japan, France, the Netherlands and Germany.^[5]

The ozone near the ground forms because of pollution. It is formed by a chemical reaction between volatile organic compounds and nitrogen oxides. These molecules are common pollutants in cities. Ozone at ground level creates smog.^[6]

Ozone Media

A prototype ozonometer built by John Smyth in 1865
Liquid ozone in a test tube
Resonance Lewis structures of the ozone molecule
General reaction equation of ozonolysis
Ozonolysis reaction of an alkene
Concentration of ozone as measured by the Nimbus-7 satellite
Total ozone concentration in June 2000 as measured by the NASA EP-TOMS satellite instrument
Levels of ozone at various altitudes and blocking of different bands of ultraviolet radiation. Essentially all UVC (100–280 nm) is blocked by dioxygen (at 100–200 nm) or by ozone (at 200–280 nm) in the atmosphere.