b.p. 77.06°C. It is used as a solvent
and in Ûavourings and perfumery.
ethyl group The organic group
CH 3 CH 2 –.
ethyl iodide See iodoethane.
ethyne (acetylene) A colourless unstable gas, C 2 H 2 , with a characteristic
sweet odour; r.d. 0.618; m.p. –80.8°C;
b.p. –84.0°C. It is the simplest member of the *alkyne series of unsaturated hydrocarbons, and is prepared
by the action of water on calcium dicarbide or by adding alcoholic potassium hydroxide to 1,2-dibromoethane.
It can be manufactured by heating
methane to 1500°C in the presence
of a catalyst. It is used in oxyacetylene welding and in the manufacture
of ethanal and ethanoic acid. Ethyne
can be polymerized easily at high
temperatures to give a range of products. The inorganic saltlike dicarbides contain the ion C 2
2– , although
ethyne itself is a neutral compound
(i.e. not a protonic acid).
eudiometer An apparatus for
measuring changes in volume of
gases during chemical reactions. A
simple example is a graduated glass
tube sealed at one end and inverted
in mercury. Wires passing into the
tube allow the gas mixture to be
sparked to initiate the reaction between gases in the tube.
europium Symbol Eu. A soft silvery
metallic element belonging to the
*lanthanoids; a.n. 63; r.a.m. 151.96;
r.d. 5.245 (20°C); m.p. 822°C; b.p.
1597°C. It occurs in small quantities
in bastanite and monazite. Two stable isotopes occur naturally: europium–151 and europium–153, both
of which are neutron absorbers. Experimental europium alloys have
been tried for nuclear-reactor parts
but until recently the metal has not
been available in sufÜcient quantities. It is widely used in the form of
the oxide in phosphors for television
screens. It was discovered by Sir
William Crookes in 1889.
A
• Information from the WebElements site
eutectic mixture A solid solution
consisting of two or more substances
and having the lowest freezing point
of any possible mixture of these components. The minimum freezing
point for a set of components is
called the eutectic point. Lowmelting-point alloys are usually
eutectic mixtures.
Evans balance See gouy balance.
evaporation The change of state
of a liquid into a vapour at a temperature below the boiling point of the
liquid. Evaporation occurs at the surface of a liquid, some of those molecules with the highest kinetic
energies escaping into the gas phase.
The result is a fall in the average kinetic energy of the molecules of the
liquid and consequently a fall in its
temperature.
exa- Symbol E. A preÜx used in the
metric system to denote 10
18 times.
For example, 10
18 metres = 1 exametre (Em).
EXAFS (extended X-ray absorption
Üne structure) Oscillations of the Xray absorption coefÜcient beyond an
absorption edge. The physical cause
of EXAFS is the modiÜcation of the
Ünal state of a photoelectron *wave
function caused by back-scattering
from atoms surrounding the excited
atom. EXAFS is used to determine
structure in chemical, solid state, or
biological systems; it is especially
useful in those systems in which it is
not possible to use diffraction techniques. EXAFS experiments are usually performed using synchrotron
radiation. It is possible to interpret
EXAFS experiments using single215
EXAFS
e
www.AzShimi.ir www.AzShimi.com
and in Ûavourings and perfumery.
ethyl group The organic group
CH 3 CH 2 –.
ethyl iodide See iodoethane.
ethyne (acetylene) A colourless unstable gas, C 2 H 2 , with a characteristic
sweet odour; r.d. 0.618; m.p. –80.8°C;
b.p. –84.0°C. It is the simplest member of the *alkyne series of unsaturated hydrocarbons, and is prepared
by the action of water on calcium dicarbide or by adding alcoholic potassium hydroxide to 1,2-dibromoethane.
It can be manufactured by heating
methane to 1500°C in the presence
of a catalyst. It is used in oxyacetylene welding and in the manufacture
of ethanal and ethanoic acid. Ethyne
can be polymerized easily at high
temperatures to give a range of products. The inorganic saltlike dicarbides contain the ion C 2
2– , although
ethyne itself is a neutral compound
(i.e. not a protonic acid).
eudiometer An apparatus for
measuring changes in volume of
gases during chemical reactions. A
simple example is a graduated glass
tube sealed at one end and inverted
in mercury. Wires passing into the
tube allow the gas mixture to be
sparked to initiate the reaction between gases in the tube.
europium Symbol Eu. A soft silvery
metallic element belonging to the
*lanthanoids; a.n. 63; r.a.m. 151.96;
r.d. 5.245 (20°C); m.p. 822°C; b.p.
1597°C. It occurs in small quantities
in bastanite and monazite. Two stable isotopes occur naturally: europium–151 and europium–153, both
of which are neutron absorbers. Experimental europium alloys have
been tried for nuclear-reactor parts
but until recently the metal has not
been available in sufÜcient quantities. It is widely used in the form of
the oxide in phosphors for television
screens. It was discovered by Sir
William Crookes in 1889.
A
• Information from the WebElements site
eutectic mixture A solid solution
consisting of two or more substances
and having the lowest freezing point
of any possible mixture of these components. The minimum freezing
point for a set of components is
called the eutectic point. Lowmelting-point alloys are usually
eutectic mixtures.
Evans balance See gouy balance.
evaporation The change of state
of a liquid into a vapour at a temperature below the boiling point of the
liquid. Evaporation occurs at the surface of a liquid, some of those molecules with the highest kinetic
energies escaping into the gas phase.
The result is a fall in the average kinetic energy of the molecules of the
liquid and consequently a fall in its
temperature.
exa- Symbol E. A preÜx used in the
metric system to denote 10
18 times.
For example, 10
18 metres = 1 exametre (Em).
EXAFS (extended X-ray absorption
Üne structure) Oscillations of the Xray absorption coefÜcient beyond an
absorption edge. The physical cause
of EXAFS is the modiÜcation of the
Ünal state of a photoelectron *wave
function caused by back-scattering
from atoms surrounding the excited
atom. EXAFS is used to determine
structure in chemical, solid state, or
biological systems; it is especially
useful in those systems in which it is
not possible to use diffraction techniques. EXAFS experiments are usually performed using synchrotron
radiation. It is possible to interpret
EXAFS experiments using single215
EXAFS
e
www.AzShimi.ir www.AzShimi.com