and associated high ionization energies (He 2370 to Rn 1040 kJ mol
–1
)
and lack of chemical reactivity. Being
monatomic the noble gases are
spherically symmetrical and have
very weak interatomic interactions
and consequent low enthalpies of vaporization. The behaviour of the
lighter members approaches that of
an ideal gas at normal temperatures;
with the heavier members increasing
polarizability and dispersion forces
lead to easier liquefaction under
pressure. Four types of ‘compound’
have been described for the noble
gases but of these only one can be
correctly described as compounds in
the normal sense. One type consists
of such species as HHe
+ , He 2
+
, Ar 2
+ ,
HeLi
+ , which form under highly energetic conditions, such as those in arcs
and sparks. They are short-lived and
only detected spectroscopically. A
second group of materials described
as inert-gas–metal compounds do not
have deÜned compositions and are
simply noble gases adsorbed onto the
surface of dispersed metal. The third
type, previously described as ‘hydrates’ are in fact clathrate compounds with the noble gas molecule
trapped in a water lattice. True compounds of the noble gases were Ürst
described in 1962 and several
Ûuorides, oxyÛuorides, Ûuoroplatinates, and Ûuoroantimonates of
*xenon are known. A few krypton
Ûuorides and a radon Ûuoride are
also known although the short halflife of radon and its intense alpha activity restrict the availability of
information. Apart from argon, the
noble gases are present in the atmosphere at only trace levels. Helium
may be found along with natural gas
(up to 7%), arising from the radioactive decay of heavier elements (via
alpha particles).
noble metal A metal characterized
by it lack of chemical reactivity, particularly to acids and atmospheric
corrosion. Examples include gold,
palladium, platinum, and rhodium.
no-bond resonance See hyperconjugation.
NOE See nuclear overhauser effect.
nonahydrate A crystalline compound that has nine moles of water
per mole of compound.
nonanoic acid (perargonic acid) A
clear oily liquid carboxylic acid, CH 3
(CH 2 ) 7 COOH; r.d. 0.9; m.p. 12.5°C;
b.p. 254°C. It is found as esters in oil
of pelargonium and certain esters are
used as Ûavourings.
nonbenzenoid aromatics Aromatic compounds that have rings
other than benzene rings. Examples
are the cyclopentadienyl anion,
C 5 H 5
– , and the tropylium cation,
C 7 H 7
+ . See also annulenes.
noncompetitive inhibition See
inhibition.
nonequilibrium statistical mechanics The statistical mechanics of
systems not in thermal equilibrium.
One of the main purposes of nonequilibrium statistical mechanics is
to calculate *transport coefÜcients
and inverse transport coefÜcients,
such as conductivity and viscosity,
from Ürst principles and to provide a
basis for transport theory. The nonequilibrium systems easiest to understand are those near thermal
equilibrium. For systems far from
equilibrium, such possibilities as
*chaos and self-organization can
arise due to nonlinearity.
nonequilibrium thermodynamics The thermodynamics of systems
not in thermal equilibrium. The nonequilibrium systems easiest to understand are those near thermal
377
nonequilibrium thermodynamics
n
www.AzShimi.ir www.AzShimi.com
–1
)
and lack of chemical reactivity. Being
monatomic the noble gases are
spherically symmetrical and have
very weak interatomic interactions
and consequent low enthalpies of vaporization. The behaviour of the
lighter members approaches that of
an ideal gas at normal temperatures;
with the heavier members increasing
polarizability and dispersion forces
lead to easier liquefaction under
pressure. Four types of ‘compound’
have been described for the noble
gases but of these only one can be
correctly described as compounds in
the normal sense. One type consists
of such species as HHe
+ , He 2
+
, Ar 2
+ ,
HeLi
+ , which form under highly energetic conditions, such as those in arcs
and sparks. They are short-lived and
only detected spectroscopically. A
second group of materials described
as inert-gas–metal compounds do not
have deÜned compositions and are
simply noble gases adsorbed onto the
surface of dispersed metal. The third
type, previously described as ‘hydrates’ are in fact clathrate compounds with the noble gas molecule
trapped in a water lattice. True compounds of the noble gases were Ürst
described in 1962 and several
Ûuorides, oxyÛuorides, Ûuoroplatinates, and Ûuoroantimonates of
*xenon are known. A few krypton
Ûuorides and a radon Ûuoride are
also known although the short halflife of radon and its intense alpha activity restrict the availability of
information. Apart from argon, the
noble gases are present in the atmosphere at only trace levels. Helium
may be found along with natural gas
(up to 7%), arising from the radioactive decay of heavier elements (via
alpha particles).
noble metal A metal characterized
by it lack of chemical reactivity, particularly to acids and atmospheric
corrosion. Examples include gold,
palladium, platinum, and rhodium.
no-bond resonance See hyperconjugation.
NOE See nuclear overhauser effect.
nonahydrate A crystalline compound that has nine moles of water
per mole of compound.
nonanoic acid (perargonic acid) A
clear oily liquid carboxylic acid, CH 3
(CH 2 ) 7 COOH; r.d. 0.9; m.p. 12.5°C;
b.p. 254°C. It is found as esters in oil
of pelargonium and certain esters are
used as Ûavourings.
nonbenzenoid aromatics Aromatic compounds that have rings
other than benzene rings. Examples
are the cyclopentadienyl anion,
C 5 H 5
– , and the tropylium cation,
C 7 H 7
+ . See also annulenes.
noncompetitive inhibition See
inhibition.
nonequilibrium statistical mechanics The statistical mechanics of
systems not in thermal equilibrium.
One of the main purposes of nonequilibrium statistical mechanics is
to calculate *transport coefÜcients
and inverse transport coefÜcients,
such as conductivity and viscosity,
from Ürst principles and to provide a
basis for transport theory. The nonequilibrium systems easiest to understand are those near thermal
equilibrium. For systems far from
equilibrium, such possibilities as
*chaos and self-organization can
arise due to nonlinearity.
nonequilibrium thermodynamics The thermodynamics of systems
not in thermal equilibrium. The nonequilibrium systems easiest to understand are those near thermal
377
nonequilibrium thermodynamics
n
www.AzShimi.ir www.AzShimi.com