neptunium seriesSee radioactive
series.Nernst, (Hermann) Walther
(1864–1941) German physical
chemist noted for his work on elec-
trochemistry and chemical thermo-
dynamics. He is remembered as the
discoverer of the third law of ther-
modynamics. Nernst was awarded
the 1920 Nobel prize for chemistry.Nernst–Einstein equation An
equation relating the limiting molar
conductivity Λm^0 (see kohlrausch’s
law) to the ionic diffusion coefÜ-
cients, devised by Nernst and Albert
*Einstein. The Nernst–Einstein equa-
tion is
Λm^0 = (F^2 /RT)(v+z+^2 D++ v–z–^2 D–),
where F is the Faraday constant, R is
the gas constant, T is the thermody-
namic temperature, v+and v–are the
number of cations and anions per
formula unit of electrolyte, z+and z–
are the valences of the ions, and D+
and D–are the diffusion coefÜcients
of the ions. An application of the
Nernst–Einstein equation is to calcu-
late the ionic diffusion coefÜcients
from experimental determinations of
conductivity.Nernst equation An equation that
relates the *electrode potential E of
an electrode that is in contact with
an ionic solution to the ionic concen-
tration c. The equation is:
E = EŠ– RTzFlnc,
where EŠis the standard electrode
potential, R is the gas constant, T is
the absolute temperature, z is the va-
lence of the ion, and F is the Faraday
constant. The equation was derived
by Walther *Nernst in 1889. It is fun-
damental to the thermodynamics of
electrochemical cells.Nernst heat theorem A state-
ment of the third law of *thermody-
namics in a restricted form given byWalter Nernst: if a chemical change
takes place between pure crystalline
solids at *absolute zero there is no
change of entropy.
nerve agentsA class of highly
toxic compounds that act by affect-
ing the action of acetylcholine, a neu-
rotransmitter regulated by the
enzyme acetylcholinesterase (AChE).
The nerve agents, which are
organophosphates, bind to AChE and
block its action. Consequently there
is nothing to stop the build up of
acetylcholine, and exposure to small
amounts of nerve gas can kill in min-
utes. There are two series of agents.
The G-serieswas produced by Ger-
man scientists in the 1930s and 40s
(the G stands for German). The main
ones are *tabun (GA), *sarin (GB),
*soman (GD), and *cyclosarin (GF). A
further series of nerve agents is the
V-series. The most common of these
is *VX, which was discovered at Por-
ton Down in the UK in 1952. Nerve
agents are classiÜed as weapons of
mass destruction by the UN.
nesquehonite A mineral form of
*magnesium carbonate trihydrate,
MgCO 3 .3H 2 O.Nessler’s reagent A solution of
mercury(II) iodide (HgI 2 ) in potassium
iodide and potassium hydroxide
named after Julius Nessler
(1827–1905). It is used in testing for
ammonia, with which it forms a
brown coloration or precipitate.neutralDescribing a compound or
solution that is neither acidic nor
basic. A neutral solution is one that
contains equal numbers of both pro-
tonated and deprotonated forms of
the solvent.
neutralizationThe process in
which an acid reacts with a base to
form a salt and water.neutron A neutral hadron that isneptunium series 368n