equilibrium; these systems are described by the *Onsager relations.
For systems far from equilibrium,
more complicated patterns, such as
*chaos and *self-organization, can
arise due to nonlinearity. Which behaviour is observed depends on the
value of certain parameters in the
system. The transition from one type
of behaviour to another as the parameters are altered occurs at *bifurcations.
nonferrous metal Any metal
other than iron or any alloy that does
not contain iron. In commercial
terms this usually means aluminium,
copper, lead, nickel, tin, zinc, or
their alloys.
nonmetal An element that is not a
*metal. Nonmetals can either be insulators or semiconductors. At low
temperatures nonmetals are poor
conductors of both electricity and
heat as few free electrons move
through the material. If the conduction band is near to the valence band
(see energy bands) it is possible for
nonmetals to conduct electricity at
high temperatures but, in contrast to
metals, the conductivity increases
with increasing temperature. Nonmetals are electronegative elements,
such as carbon, nitrogen, oxygen,
phosphorus, sulphur, and the halogens. They form compounds that
contain negative ions or covalent
bonds. Their oxides are either neutral or acidic.
nonpolar compound A compound that has covalent molecules
with no permanent dipole moment.
Examples of nonpolar compounds
are methane and benzene.
nonpolar solvent See solvent.
nonreducing sugar A sugar that
cannot donate electrons to other
molecules and therefore cannot act
as a reducing agent. Sucrose is the
most common nonreducing sugar.
The linkage between the glucose and
fructose units in sucrose, which involves aldehyde and ketone groups,
is responsible for the inability of sucrose to act as a *reducing sugar.
nonrelativistic quantum theory
See quantum theory.
nonrenewable energy sources
See renewable energy sources.
nonstoichiometric compound
(Berthollide compound) A chemical
compound in which the elements do
not combine in simple ratios. For example, rutile (titanium(IV) oxide) is
often deÜcient in oxygen, typically
having a formula TiO 1.8 .
noradrenaline (norepinephrine) A
hormone produced by the adrenal
glands and also secreted from nerve
endings in the sympathetic nervous
system as a chemical transmitter of
nerve impulses. Many of its general
actions are similar to those of
*adrenaline, but it is more concerned
with maintaining normal body activity than with preparing the body for
emergencies.
Nordhausen sulphuric acid See
disulphuric(vi) acid.
norepinephrine See noradrenaline.
normal Having a concentration of
one gram equivalent per dm
3
.
normal mode of vibration A
basic vibration of a polyatomic molecule. All vibrational motion of a
polyatomic molecule can be treated
as a superposition of the normal
modes of vibration of the molecule.
If N is the number of atoms in a molecule, the number of modes of vibration is 3N – 5 for a linear molecule
and 3N – 6 for a nonlinear molecule.
Each of these vibrational modes has a
characteristic frequency, although it
nonferrous metal
378
n
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For systems far from equilibrium,
more complicated patterns, such as
*chaos and *self-organization, can
arise due to nonlinearity. Which behaviour is observed depends on the
value of certain parameters in the
system. The transition from one type
of behaviour to another as the parameters are altered occurs at *bifurcations.
nonferrous metal Any metal
other than iron or any alloy that does
not contain iron. In commercial
terms this usually means aluminium,
copper, lead, nickel, tin, zinc, or
their alloys.
nonmetal An element that is not a
*metal. Nonmetals can either be insulators or semiconductors. At low
temperatures nonmetals are poor
conductors of both electricity and
heat as few free electrons move
through the material. If the conduction band is near to the valence band
(see energy bands) it is possible for
nonmetals to conduct electricity at
high temperatures but, in contrast to
metals, the conductivity increases
with increasing temperature. Nonmetals are electronegative elements,
such as carbon, nitrogen, oxygen,
phosphorus, sulphur, and the halogens. They form compounds that
contain negative ions or covalent
bonds. Their oxides are either neutral or acidic.
nonpolar compound A compound that has covalent molecules
with no permanent dipole moment.
Examples of nonpolar compounds
are methane and benzene.
nonpolar solvent See solvent.
nonreducing sugar A sugar that
cannot donate electrons to other
molecules and therefore cannot act
as a reducing agent. Sucrose is the
most common nonreducing sugar.
The linkage between the glucose and
fructose units in sucrose, which involves aldehyde and ketone groups,
is responsible for the inability of sucrose to act as a *reducing sugar.
nonrelativistic quantum theory
See quantum theory.
nonrenewable energy sources
See renewable energy sources.
nonstoichiometric compound
(Berthollide compound) A chemical
compound in which the elements do
not combine in simple ratios. For example, rutile (titanium(IV) oxide) is
often deÜcient in oxygen, typically
having a formula TiO 1.8 .
noradrenaline (norepinephrine) A
hormone produced by the adrenal
glands and also secreted from nerve
endings in the sympathetic nervous
system as a chemical transmitter of
nerve impulses. Many of its general
actions are similar to those of
*adrenaline, but it is more concerned
with maintaining normal body activity than with preparing the body for
emergencies.
Nordhausen sulphuric acid See
disulphuric(vi) acid.
norepinephrine See noradrenaline.
normal Having a concentration of
one gram equivalent per dm
3
.
normal mode of vibration A
basic vibration of a polyatomic molecule. All vibrational motion of a
polyatomic molecule can be treated
as a superposition of the normal
modes of vibration of the molecule.
If N is the number of atoms in a molecule, the number of modes of vibration is 3N – 5 for a linear molecule
and 3N – 6 for a nonlinear molecule.
Each of these vibrational modes has a
characteristic frequency, although it
nonferrous metal
378
n
www.AzShimi.ir www.AzShimi.com