dissociation of a molecule by extrap-
olation from observed band spectra.
The dissociation energy D 0 is equal to
the sum of the vibrational quanta ∆G,
where ∆G represents the energy be-
tween two successive vibrational
states. This means that D 0 is approxi-
mately equal to the area under the
curve of ∆G plotted against the vibra-
tional quantum number v. If theÜrst
few vibrational quanta are observed,
an approximate value of D 0 can be
obtained by a linear extrapolation of
this curve. If a sufÜcient number of
vibrational quanta have been ob-
served, a considerable improvement
in the value of D 0 can be obtained by
taking the curvature of the ∆G curve
into account by quadratic (and/or)
higher terms. The technique was put
forward by R. T. Birge and H. Sponer
in 1926.
Birkeland–Eyde process A
process for theÜxation of nitrogen
by passing air through an electric
arc to produce nitrogen oxides. It
was introduced in 1903 by the Nor-
wegian chemists Kristian Birkeland
(1867–1913) and Samuel Eyde
(1866–1940). The process is economic
only if cheap hydroelectricity is avail-
able.
bisecting See conformation.
bismuth Symbol Bi. A white crys-
talline metal with a pinkish tinge be-
longing to *group 15 (formerly VB) of
the periodic table; a.n. 83; r.a.m.
208.98; r.d. 9.78; m.p. 271.3°C; b.p.
1560 °C. The most important ores are
bismuthinite (Bi 2 S 3 ) and bismite
(Bi 2 O 3 ). Peru, Japan, Mexico, Bolivia,
and Canada are major producers. The
metal is extracted by carbon reduc-
tion of its oxide. Bismuth is the most
diamagnetic of all metals and its
thermal conductivity is lower than
any metal except mercury. The metal
has a high electrical resistance and a
high Hall effect when placed in mag-
neticÜelds. It is used to make low-
melting-point casting alloys with tin
and cadmium. These alloys expand
on solidiÜcation to give clear replica-
tion of intricate features. It is also
used to make thermally activated
safety devices forÜre-detection and
sprinkler systems. More recent appli-
cations include its use as a catalyst
for making acrylicÜbres, as a con-
stituent of malleable iron, as a car-
rier of uranium–235 fuel in nuclear
reactors, and as a specialized thermo-
couple material. Bismuth compounds
(when lead-free) are used for cosmet-
ics and medical preparations. It is at-
tacked by oxidizing acids, steam (at
high temperatures), and by moist
halogens. It burns in air with a blue
Ûame to produce yellow oxide fumes.
C. G. JunineÜrst demonstrated that it
was different from lead in 1753.
A- Information from the WebElements site
bisphosphonates(diphospho-
nates)A class of medical drugs used
in the treatment of osteoporosis and
other conditions that involve fragile
bones. The bisphosphonates attack
osteoclasts (i.e. the bone cells that
break down bone tissue). The general
formula is O 3 P–C(R^1 R^3 )–PO 3. The side
chain R^1 is a simple group (–H, –OH,
–Cl). R^2 is usually a longer chain (e.g.
–S–C 6 H 4 –Cl or –(CH 2 ) 5 –NH 2.
bistabilityThe ability of a system
to exist in two steady states. Bistabil-
ity is a necessary condition for oscil-
lations to occur in chemical
reactions. The two steady states of a
bistable system are not states of ther-
modynamic equilibrium, as they are
associated with conditions far from
equilibrium. Chemical reactions in-
volving bistability jump suddenly
from one state to the other state
when a certain concentration of one
of the participants in the reaction is73 bistability
b