liquid air. It is used in metallurgical
processes, in high-temperature
Ûames (e.g. for welding), and in
breathing apparatus. The common
form is diatomic (dioxygen, O 2 );
there is also a reactive allotrope
*ozone (O 3 ). Chemically, oxygen reacts with most other elements forming *oxides. The element was
discovered by Joseph Priestley in
1774.
A
• Information from the WebElements site
oxygenates Oxygen-containing
organic compounds, such as ethanol
and acetone, present in motor
fuels.
oxyhaemoglobin See haemoglobin.
ozonation The formation of
*ozone (O 3 ) in the earth’s atmosphere. In the upper atmosphere
(stratosphere) about 20–50 km above
the surface of the earth, oxygen molecules (O 2 ) dissociate into their constituent atoms under the inÛuence of
ultraviolet light of short wavelength
(below about 240 nm). These atoms
combine with oxygen molecules to
form ozone (see ozone layer). Ozone
is also formed in the lower atmosphere from nitrogen oxides and
other pollutants by photochemical
reactions (see photochemical smog).
ozone (trioxygen) A colourless gas,
O 3 , soluble in cold water and in alkalis; m.p. –192.7°C; b.p. –111.9°C. Liquid ozone is dark blue in colour and
is diamagnetic (dioxygen, O 2 , is paramagnetic). The gas is made by passing oxygen through a silent electric
discharge and is usually used in mixtures with oxygen. It is produced in
the stratosphere by the action of
high-energy ultraviolet radiation on
oxygen and its presence there acts as
a screen for ultraviolet radiation (see
ozone layer). Ozone is also one of
the greenhouse gases (see greenhouse effect). It is a powerful oxidizing agent and is used to form
ozonides by reaction with alkenes
and subsequently by hydrolysis to
carbonyl compounds.
ozone hole See ozone layer.
ozone layer (ozonosphere) A layer
of the *earth’s atmosphere in which
most of the atmosphere’s ozone is
concentrated. It occurs 15–50 km
above the earth’s surface and is virtually synonymous with the stratosphere. In this layer most of the sun’s
ultraviolet radiation is absorbed by
the ozone molecules, causing a rise
in the temperature of the stratosphere and preventing vertical mixing
so that the stratosphere forms a stable layer. By absorbing most of the
solar ultraviolet radiation the ozone
layer protects living organisms on
earth. The fact that the ozone layer is
thinnest at the equator is believed to
account for the high equatorial incidence of skin cancer as a result of exposure to unabsorbed solar
ultraviolet radiation. In the 1980s it
was found that depletion of the
ozone layer was occurring over both
the poles, creating ozone holes. This
is thought to have been caused by a
series of complex photochemical reactions involving nitrogen oxides
produced from aircraft and, more seriously, *chloroÛuorocarbons (CFCs)
and *halons. CFCs rise to the stratosphere, where they react with ultraviolet light to release chlorine atoms;
these atoms, which are highly reactive, catalyse the destruction of
ozone. Use of CFCs is now much reduced in an effort to reverse this
human-induced damage to the ozone
layer.
ozonides 1. A group of compounds
formed by reaction of ozone with alkali metal hydroxides and formally
395
ozonides
o
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processes, in high-temperature
Ûames (e.g. for welding), and in
breathing apparatus. The common
form is diatomic (dioxygen, O 2 );
there is also a reactive allotrope
*ozone (O 3 ). Chemically, oxygen reacts with most other elements forming *oxides. The element was
discovered by Joseph Priestley in
1774.
A
• Information from the WebElements site
oxygenates Oxygen-containing
organic compounds, such as ethanol
and acetone, present in motor
fuels.
oxyhaemoglobin See haemoglobin.
ozonation The formation of
*ozone (O 3 ) in the earth’s atmosphere. In the upper atmosphere
(stratosphere) about 20–50 km above
the surface of the earth, oxygen molecules (O 2 ) dissociate into their constituent atoms under the inÛuence of
ultraviolet light of short wavelength
(below about 240 nm). These atoms
combine with oxygen molecules to
form ozone (see ozone layer). Ozone
is also formed in the lower atmosphere from nitrogen oxides and
other pollutants by photochemical
reactions (see photochemical smog).
ozone (trioxygen) A colourless gas,
O 3 , soluble in cold water and in alkalis; m.p. –192.7°C; b.p. –111.9°C. Liquid ozone is dark blue in colour and
is diamagnetic (dioxygen, O 2 , is paramagnetic). The gas is made by passing oxygen through a silent electric
discharge and is usually used in mixtures with oxygen. It is produced in
the stratosphere by the action of
high-energy ultraviolet radiation on
oxygen and its presence there acts as
a screen for ultraviolet radiation (see
ozone layer). Ozone is also one of
the greenhouse gases (see greenhouse effect). It is a powerful oxidizing agent and is used to form
ozonides by reaction with alkenes
and subsequently by hydrolysis to
carbonyl compounds.
ozone hole See ozone layer.
ozone layer (ozonosphere) A layer
of the *earth’s atmosphere in which
most of the atmosphere’s ozone is
concentrated. It occurs 15–50 km
above the earth’s surface and is virtually synonymous with the stratosphere. In this layer most of the sun’s
ultraviolet radiation is absorbed by
the ozone molecules, causing a rise
in the temperature of the stratosphere and preventing vertical mixing
so that the stratosphere forms a stable layer. By absorbing most of the
solar ultraviolet radiation the ozone
layer protects living organisms on
earth. The fact that the ozone layer is
thinnest at the equator is believed to
account for the high equatorial incidence of skin cancer as a result of exposure to unabsorbed solar
ultraviolet radiation. In the 1980s it
was found that depletion of the
ozone layer was occurring over both
the poles, creating ozone holes. This
is thought to have been caused by a
series of complex photochemical reactions involving nitrogen oxides
produced from aircraft and, more seriously, *chloroÛuorocarbons (CFCs)
and *halons. CFCs rise to the stratosphere, where they react with ultraviolet light to release chlorine atoms;
these atoms, which are highly reactive, catalyse the destruction of
ozone. Use of CFCs is now much reduced in an effort to reverse this
human-induced damage to the ozone
layer.
ozonides 1. A group of compounds
formed by reaction of ozone with alkali metal hydroxides and formally
395
ozonides
o
www.AzShimi.ir www.AzShimi.com