CRC Handbook of Chemistry and Physics, 86th Edition

4-14 The Elements
Laboratory. The isotope produced was the 20-hour 255 Fm.
During 1953 and early 1954, while discovery of elements 99
and 100 was withheld from publication for security reasons, a
group from the Nobel Institute of Physics in Stockholm bombarded
238 U with 16 O ions, and isolated a 30-min α-emitter,
which they ascribed to 250 100, without claiming discovery of
the element. This isotope has since been identified positively,
and the 30-min half-life confirmed. The chemical properties
of fermium have been studied solely with tracer amounts,
and in normal aqueous media only the (III) oxidation state
appears to exist. The isotope 254 Fm and heavier isotopes can
be produced by intense neutron irradiation of lower elements
such as plutonium by a process of successive neutron capture
interspersed with beta decays until these mass numbers and
atomic numbers are reached. Twenty isotopes and isomers of
fermium are known to exist. 257 Fm, with a half-life of about
100.5 days, is the longest lived. 250 Fm, with a half-life of 30 min,
has been shown to be a product of decay of Element 254 102.
It was by chemical identification of 250 Fm that production
of Element 102 (nobelium) was confirmed. Fermium would
probably have chemical properties resembling erbium.
Fluorine — (L. and F. fluere, flow, or flux), F; at. wt. 18.9984032(5);
at. no. 9; m.p. –219.62°C (1 atm); b.p. –188.12°C (1 atm); t c
–129.02°C; density 1.696 g/L (0°C, 1 atm); liq. den. at b.p. 1.50
g/cm 3 ; valence 1. In 1529, Georgius Agricola described the use
of fluorspar as a flux, and as early as 1670 Schwandhard found
that glass was etched when exposed to fluorspar treated with
acid. Scheele and many later investigators, including Davy,
Gay-Lussac, Lavoisier, and Thenard, experimented with hydrofluoric
acid, some experiments ending in tragedy. The element
was finally isolated in 1886 by Moisson after nearly 74
years of continuous effort. Fluorine occurs chiefly in fluorspar
(CaF 2 ) and cryolite (Na 2 AlF 6 ), and is in topaz and other minerals.
It is a member of the halogen family of elements, and is
obtained by electrolyzing a solution of potassium hydrogen
fluoride in anhydrous hydrogen fluoride in a vessel of metal or
transparent fluorspar. Modern commercial production methods
are essentially variations on the procedures first used by
Moisson. Fluorine is the most electronegative and reactive
of all elements. It is a pale yellow, corrosive gas, which reacts
with practically all organic and inorganic substances. Finely
divided metals, glass, ceramics, carbon, and even water burn
in fluorine with a bright flame. Until World War II, there was
no commercial production of elemental fluorine. The atom
bomb project and nuclear energy applications, however, made
it necessary to produce large quantities. Safe handling techniques
have now been developed and it is possible at present
to transport liquid fluorine by the ton. Fluorine and its compounds
are used in producing uranium (from the hexafluoride)
and more than 100 commercial fluorochemicals, including
many well-known high-temperature plastics. Hydrofluoric
acid is extensively used for etching the glass of light bulbs, etc.
Fluorochloro hydrocarbons have been extensively used in air
conditioning and refrigeration. However, in recent years the
U.S. and other countries have been phasing out ozone-depleting
substances, such as the fluorochloro hydrocarbons that
have been used in these applications. It has been suggested
that fluorine might be substituted for hydrogen wherever it
occurs in organic compounds, which could lead to an astronomical
number of new fluorine compounds. The presence
of fluorine as a soluble fluoride in drinking water to the extent
of 2 ppm may cause mottled enamel in teeth, when used
by children acquiring permanent teeth; in smaller amounts,
however, fluorides are said to be beneficial and used in water
supplies to prevent dental cavities. Elemental fluorine has
been studied as a rocket propellant as it has an exceptionally
high specific impulse value. Compounds of fluorine with rare
gases have now been confirmed. Fluorides of xenon, radon,
and krypton are among those known. Elemental fluorine and
the fluoride ion are highly toxic. The free element has a characteristic
pungent odor, detectable in concentrations as low
as 20 ppb, which is below the safe working level. The recommended
maximum allowable concentration for a daily 8-hour
time-weighted exposure is 1 ppm. Fluorine is known to have
fourteen isotopes.
Francium — (France), Fr; at. no. 87; at. wt. [223]; m.p. 27°C; valence
1. Discovered in 1939 by Mlle. Marguerite Perey of the
Curie Institute, Paris. Francium, the heaviest known member
of the alkali metal series, occurs as a result of an alpha
disintegration of actinium. It can also be made artificially by
bombarding thorium with protons. While it occurs naturally
in uranium minerals, there is probably less than an ounce of
francium at any time in the total crust of the earth. It has the
highest equivalent weight of any element, and is the most unstable
of the first 101 elements of the periodic system. Thirtysix
isotopes and isomers of francium are recognized. The longest
lived 223 Fr(Ac, K), a daughter of 227 Ac, has a half-life of
21.8 min. This is the only isotope of francium occurring in
nature. Because all known isotopes of francium are highly unstable,
knowledge of the chemical properties of this element
comes from radiochemical techniques. No weighable quantity
of the element has been prepared or isolated. The chemical
properties of francium most closely resemble cesium. In 1996,
researchers Orozco, Sprouse, and co-workers at the State
University of New York, Stony Brook, reported that they had
produced francium atoms by bombarding 18 O atoms at a gold
target heated almost to its melting point. Collisions between
gold and oxygen nuclei created atoms of francium-210 which
had 87 protons and 123 neutrons. This team reported they
had generated about 1 million francium-210 ions per second
and held 1000 or more atoms at a time for about 20 secs. in a
magnetic trap they had devised before the atoms decayed or
escaped. Enough francium was trapped so that a video camera
could capture the light given off by the atoms as they fluoresced.
A cluster of about 10,000 francium atoms appeared as
a glowing sphere about 1 mm in diameter. It is thought that
the francium atoms could serve as miniature laboratoires for
probing interactions between electrons and quarks.
Gadolinium — (gadolinite, a mineral named for Gadolin, a Finnish
chemist), Gd; at. wt. 157.25(3); at. no. 64; m.p. 1313°C; b.p.
3273°C; sp. gr. 7.901 (25°C); valence 3. Gadolinia, the oxide
of gadolinium, was separated by Marignac in 1880 and Lecoq
de Boisbaudran independently isolated the element from
Mosander’s “yttria” in 1886. The element was named for the
mineral gadolinite from which this rare earth was originally
obtained. Gadolinium is found in several other minerals, including
monazite and bastnasite, which are of commercial importance.
The element has been isolated only in recent years.
With the development of ion-exchange and solvent extraction
techniques, the availability and price of gadolinium and
the other rare-earth metals have greatly improved. Thirtyone
isotopes and isomers of gadolinium are now recognized;
seven are stable and occur naturally. The metal can be prepared
by the reduction of the anhydrous fluoride with metallic
calcium. As with other related rare-earth metals, it is silvery