B
Babbit metal Any of a group of related alloys used for making bearings. They consist of tin containing
antimony (about 10%) and copper
(1–2%), and often lead. The original
alloy was invented in 1839 by the US
inventor Isaac Babbit (1799–1862).
Babo’s law The vapour pressure of
a liquid is decreased when a solute is
added, the amount of the decrease
being proportional to the amount of
solute dissolved. The law was discovered in 1847 by the German chemist
Lambert Babo (1818–99). See also
raoult’s law.
backbiting A rearrangement that
can occur in some *polymerization
reactions involving free radicals. A
radical that has an unpaired electron
at the end of the chain changes into
a radical with the unpaired electron
elsewhere along the chain, the new
radical being more stable than the
one from which it originates. For example, the radical
RCH 2 CH 2 CH 2 CH 2 CH 2 CH 2
.
may change into
RCH 2 CH . CH 2 CH 2 CH 2 CH 3
The rearrangement is equivalent to
a hydrogen atom being transferred
within the molecule. The new unpaired electron initiates further
polymerization, with the production of polymers with butyl
(CH 3 CH 2 CH 2 CH 2 –) side chains.
back donation A form of chemical
bonding in which a *ligand forms a
sigma bond to an atom or ion by donating a pair of electrons, and the
central atom donates electrons back
by overlap of its d-orbitals with
empty p- or d-orbitals on the ligand.
It occurs, for example, in metal carbonyls.
back e.m.f. An electromotive force
that opposes the main current Ûow
in a circuit. For example, in an electric cell, *polarization causes a back
e.m.f. to be set up by chemical
means.
background radiation Low intensity *ionizing radiation present on
Backbiting
R
C
H 2
C
H 2
CH 2
CH 2
C
H 2
H 2 C
R
CH
C
H 2
CH 2
CH 2
C
H 2
C
H 3
R
C
H 2
C
H 2
C
H 2
C
H 2
C
H 2
CH 2
R
CH
C
H 2
C
H 2
C
H 2
C
H 2
CH 3
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