dissociation of a molecule by extrapolation from observed band spectra.
The dissociation energy D 0 is equal to
the sum of the vibrational quanta ∆G,
where ∆G represents the energy between two successive vibrational
states. This means that D 0 is approximately equal to the area under the
curve of ∆G plotted against the vibrational quantum number v. If the Ürst
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 observed, 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 the Üxation of nitrogen
by passing air through an electric
arc to produce nitrogen oxides. It
was introduced in 1903 by the Norwegian chemists Kristian Birkeland
(1867–1913) and Samuel Eyde
(1866–1940). The process is economic
only if cheap hydroelectricity is available.
bisecting See conformation.
bismuth Symbol Bi. A white crystalline metal with a pinkish tinge belonging 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 reduction 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 magnetic Üelds. It is used to make lowmelting-point casting alloys with tin
and cadmium. These alloys expand
on solidiÜcation to give clear replication of intricate features. It is also
used to make thermally activated
safety devices for Üre-detection and
sprinkler systems. More recent applications include its use as a catalyst
for making acrylic Übres, as a constituent of malleable iron, as a carrier of uranium–235 fuel in nuclear
reactors, and as a specialized thermocouple material. Bismuth compounds
(when lead-free) are used for cosmetics and medical preparations. It is attacked 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. Junine Ürst demonstrated that it
was different from lead in 1753.
A
• Information from the WebElements site
bisphosphonates (diphosphonates) 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 .
bistability The ability of a system
to exist in two steady states. Bistability is a necessary condition for oscillations to occur in chemical
reactions. The two steady states of a
bistable system are not states of thermodynamic equilibrium, as they are
associated with conditions far from
equilibrium. Chemical reactions involving bistability jump suddenly
from one state to the other state
when a certain concentration of one
of the participants in the reaction is
73
bistability
b
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The dissociation energy D 0 is equal to
the sum of the vibrational quanta ∆G,
where ∆G represents the energy between two successive vibrational
states. This means that D 0 is approximately equal to the area under the
curve of ∆G plotted against the vibrational quantum number v. If the Ürst
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 observed, 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 the Üxation of nitrogen
by passing air through an electric
arc to produce nitrogen oxides. It
was introduced in 1903 by the Norwegian chemists Kristian Birkeland
(1867–1913) and Samuel Eyde
(1866–1940). The process is economic
only if cheap hydroelectricity is available.
bisecting See conformation.
bismuth Symbol Bi. A white crystalline metal with a pinkish tinge belonging 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 reduction 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 magnetic Üelds. It is used to make lowmelting-point casting alloys with tin
and cadmium. These alloys expand
on solidiÜcation to give clear replication of intricate features. It is also
used to make thermally activated
safety devices for Üre-detection and
sprinkler systems. More recent applications include its use as a catalyst
for making acrylic Übres, as a constituent of malleable iron, as a carrier of uranium–235 fuel in nuclear
reactors, and as a specialized thermocouple material. Bismuth compounds
(when lead-free) are used for cosmetics and medical preparations. It is attacked 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. Junine Ürst demonstrated that it
was different from lead in 1753.
A
• Information from the WebElements site
bisphosphonates (diphosphonates) 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 .
bistability The ability of a system
to exist in two steady states. Bistability is a necessary condition for oscillations to occur in chemical
reactions. The two steady states of a
bistable system are not states of thermodynamic equilibrium, as they are
associated with conditions far from
equilibrium. Chemical reactions involving bistability jump suddenly
from one state to the other state
when a certain concentration of one
of the participants in the reaction is
73
bistability
b
www.AzShimi.ir www.AzShimi.com