F

FAB mass spectroscopy See fast-
atom bombardment mass spec-
troscopy.

face-centred cubic (f.c.c.)See
cubic crystal.

fac-isomer See isomerism.

FAD (Ûavin adenine dinucleotide)A
coenzyme important in various bio-
chemical reactions. It comprises a
phosphorylated vitamin B 2 (ri-
boÛavin) molecule linked to the nu-
cleotide adenine monophosphate
(AMP). FAD is usually tightly bound
to the enzyme forming a Ûavopro-
tein. It functions as a hydrogen ac-
ceptor in dehydrogenation reactions,
being reduced to FADH 2. This in turn
is oxidized to FAD by the electron
transport chain, thereby generating
ATP (two molecules of ATP per mol-
ecule of FADH 2 ).

Fahrenheit, Gabriel Daniel
(1686–1736) German physicist, who
became an instrument maker in Am-
sterdam. In 1714 he developed the
mercury-in-glass thermometer, and
devised a temperature scale to go
with it (see fahrenheit scale).

Fahrenheit scale A temperature
scale in which (by modern deÜnition)
the temperature of boiling water is
taken as 212 degrees and the temper-
ature of melting ice as 32 degrees. It
was invented in 1714 by G. D.
*Fahrenheit, who set the zero at the
lowest temperature he knew how to
obtain in the laboratory (by mixing
ice and common salt) and took his
own body temperature as 96°F. The
scale is no longer in scientiÜc use. To

convert to the *Celsius scale the for-

mula is C =5(F – 32)/9.

Fajan’s method See adsorption

indicator.

Fajans’ rulesRules indicating the

extent to which an ionic bond has co-

valent character caused by polariza-

tion of the ions. Covalent character is

more likely if:

(1) the charge of the ions is high;

(2) the positive ion is small or the

negative ion is large;

(3) the positive ion has an outer elec-

tron conÜguration that is not a noble-

gas conÜguration.

The rules were introduced by the

Polish-born US chemist Kasimir Fa-

jans (1887–1975).

fall-out1.(radioactive fall-out)

Radioactive particles deposited from

the atmosphere either from a nu-

clear explosion or from a nuclear ac-

cident. Local fall-out, within 250 km

of an explosion, falls within a few

hours of the explosion. Tropospheric

fall-outconsists ofÜne particles de-

posited all round the earth in the ap-

proximate latitude of the explosion

within about one week. Stratospheric

fall-outmay fall anywhere on earth

over a period of years. The most dan-

gerous radioactive isotopes in fall-out

are theÜssion fragments iodine–131

and strontium–90. Both can be taken

up by grazing animals and passed on

to human populations in milk, milk

products, and meat. Iodine–131 accu-

mulates in the thyroid gland and

strontium–90 accumulates in bones.

2.(chemical fall-out) Hazardous

chemicals discharged into and subse-

quently released from the atmos-