equilibrium; these systems are de-
scribed by the *Onsager relations.
For systems far from equilibrium,
more complicated patterns, such as
*chaos and *self-organization, can
arise due to nonlinearity. Which be-
haviour is observed depends on the
value of certain parameters in the
system. The transition from one type
of behaviour to another as the para-
meters are altered occurs at *bifurca-
tions.
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.
nonmetalAn element that is not a
*metal. Nonmetals can either be in-
sulators or semiconductors. At low
temperatures nonmetals are poor
conductors of both electricity and
heat as few free electrons move
through the material. If the conduc-
tion 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. Non-
metals are electronegative elements,
such as carbon, nitrogen, oxygen,
phosphorus, sulphur, and the halo-
gens. They form compounds that
contain negative ions or covalent
bonds. Their oxides are either neu-
tral or acidic.nonpolar compoundA com-
pound that has covalent molecules
with no permanent dipole moment.
Examples of nonpolar compounds
are methane and benzene.
nonpolar solventSee solvent.nonreducing sugar A sugar that
cannot donate electrons to other
molecules and therefore cannot act
as a reducing agent. Sucrose is themost common nonreducing sugar.
The linkage between the glucose and
fructose units in sucrose, which in-
volves aldehyde and ketone groups,
is responsible for the inability of su-
crose 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 ex-
ample, rutile (titanium(IV) oxide) is
often deÜcient in oxygen, typically
having a formula TiO1.8.
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 activ-
ity than with preparing the body for
emergencies.Nordhausen sulphuric acid See
disulphuric(vi) acid.
norepinephrine See noradrena-
line.
normalHaving a concentration of
one gram equivalent per dm^3.
normal mode of vibrationA
basic vibration of a polyatomic mol-
ecule. 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 mol-
ecule, the number of modes of vibra-
tion is 3N– 5 for a linear molecule
and 3N– 6 for a nonlinear molecule.
Each of these vibrational modes has a
characteristic frequency, although itnonferrous metal 378n