B

Babbit metalAny of a group of re-

lated alloys used for making bear-

ings. 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 discov-

ered in 1847 by the German chemist

Lambert Babo (1818–99). See also

raoult’s law.

backbitingA 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 ex-

ample, 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 un-

paired electron initiates further

polymerization, with the produc-

tion of polymers with butyl

(CH 3 CH 2 CH 2 CH 2 –) side chains.

back donationA form of chemical

bonding in which a *ligand forms a

sigma bond to an atom or ion by do-

nating 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 car-

bonyls.

back e.m.f.An electromotive force

that opposes the main currentÛow

in a circuit. For example, in an elec-

tric cell, *polarization causes a back

e.m.f. to be set up by chemical

means.

background radiation Low inten-

sity *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

3 CH

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