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Chromium
is a chemical element which has the symbol Cr and atomic number 24. It is the first element
in Group 6. It is a steely-gray, lustrous, hard and brittle metal which takes a high polish, resists
tarnishing, and has a high melting point. The name of the element is derived from
the Greek word "chrōma" (τρώμα), meaning colour, because many of its compounds are
intensely coloured.
Chromium oxide was used by the Chinese in the Qin dynasty over 2,000 years ago to coat metal
weapons found with the Terracotta Army. Chromium was discovered as an element after it came
to the attention of the western world in the red crystalline mineral crocoite (lead(II) chromate),
discovered in 1761 and initially used as a pigment. Louis Nicolas Vauquelin first isolated
chromium metal from this mineral in 1797. Since Vauquelin's first production of metallic
chromium, small amounts of native (free) chromium metal have been discovered in rare
minerals, but these are not used commercially. Instead, nearly all chromium is commercially
extracted from the single commercially viable ore chromite, which is iron chromium oxide
(FeCr2O4). Chromite is also now the chief source of chromium for chromium pigments.
Chromium metal and ferrochromium alloy are commercially produced from chromite
by silicothermic oraluminothermic reactions, or by roasting and leaching processes. Chromium
metal has proven of high value due to its high corrosion resistance and hardness. A major
development was the discovery that steel could be made highly resistant to corrosion and
discoloration by adding metallic chromium to formstainless steel. This application, along
with chrome plating (electroplating with chromium) currently comprise 85% of the commercial
use for the element, with applications for chromium compounds forming the remainder.
Trivalent chromium (Cr(III)) ion is possibly required in trace amounts
for sugar and lipid metabolism, although the issue remains in debate. In larger amounts and in
different forms, chromium can be toxic and carcinogenic. The most prominent example of toxic
chromium is hexavalent chromium (Cr(VI)). Abandoned chromium production sites often
require environmental cleanup.
Weapons found in burial pits dating from the late 3rd century B.C. Qin Dynasty of the Terracotta
Army nearXi'an, China have been analyzed by archaeologists. Although buried more than 2,000
years ago, the ancientbronze tips of crossbow bolts and swords found at the site showed
unexpectedly little corrosion, possibly because the bronze was deliberately coated with a thin
layer of chromium oxide.]However, this oxide layer was not chromium metal or chrome plating
as we know it.
Chromium minerals as pigments came to the attention of the west in the 18th century. On 26 July
1761,Johann Gottlob Lehmann found an orange-red mineral in the Beryozovskoye mines in
the Ural Mountains which he named Siberian red lead. Though misidentified as
a lead compound with selenium and iron components, the mineral was in fact crocoite (lead
chromate) with a formula of PbCrO4.
In 1770, Peter Simon Pallas visited the same site as Lehmann and found a red lead mineral that
had useful properties as a pigment in paints. The use of Siberian red lead as a paint pigment then
developed rapidly. A bright yellow pigment made from crocoite also became fashionable.
The red colour of rubies is from a small amount of chromium.
In 1797, Louis Nicolas Vauquelin received samples of crocoite ore. He produced chromium
trioxide (CrO3) by mixing crocoite with hydrochloric acid. In 1798, Vauquelin discovered that he
could isolate metallic chromium by heating the oxide in a charcoal oven, making him the
discoverer of the element. Vauquelin was also able to detect traces of chromium in
precious gemstones, such as ruby or emerald.
During the 1800s, chromium was primarily used as a component of paints and in tanning salts.
At first, crocoite fromRussia was the main source, but in 1827, a larger chromite deposit was
discovered near Baltimore, United States. This made the United States the largest producer of
chromium products till 1848 when large deposits of chromite were found near Bursa, Turkey.[10]
Chromium is also known for its luster when polished. It is used as a protective and decorative
coating on car parts, plumbing fixtures, furniture parts and many other items, usually applied
by electroplating. Chromium was used for electroplating as early as 1848, but this use only
became widespread with the development of an improved process in 1924.
Metal alloys now account for 85% of the use of chromium. The remainder is used in
the chemical industry and refractory and foundry industries.
Metallurgy
The strengthening effect of forming stable metal carbides at the grain boundaries and the strong
increase in corrosion resistance made chromium an important alloying material for steel.
The high-speed tool steelscontain between 3 and 5% chromium. Stainless steel, the main
corrosion-proof metal alloy, is formed when chromium is added to iron in sufficient
concentrations, usually above 11%. For its formation, ferrochromium is added to the molten iron.
Also nickel-based alloys increase in strength due to the formation of discrete, stable metal
carbide particles at the grain boundaries. For example, Inconel 718 contains 18.6% chromium.
Because of the excellent high-temperature properties of these nickel superalloys, they are used
in jet enginesand gas turbines in lieu of common structural materials
The relative high hardness and corrosion resistance of unalloyed chromium makes it a good
surface coating, being still the most "popular" metal coating with unparalleled combined
durability. A thin layer of chromium is deposited on pretreated metallic surfaces
by electroplating techniques. There are two deposition methods: Thin, below 1 µm thickness,
layers are deposited by chrome plating, and are used for decorative surfaces. If wear-resistant
surfaces are needed then thicker chromium layers are deposited. Both methods normally use
acidic chromate or dichromate solutions. To prevent the energy-consuming change in oxidation
state, the use of chromium(III) sulfate is under development, but for most applications, the
established process is used
In the chromate conversion coating process, the strong oxidative properties of chromates are
used to deposit a protective oxide layer on metals like aluminium, zinc and cadmium.
This passivation and the self-healing properties by the chromate stored in the chromate
conversion coating, which is able to migrate to local defects, are the benefits of this coating
method. Because of environmental and health regulations on chromates, alternative coating
method are under development
Anodizing of aluminium is another electrochemical process, which does not lead to the
deposition of chromium, but uses chromic acid as electrolyte in the solution. During anodization,
an oxide layer is formed on the aluminium. The use of chromic acid, instead of the normally
used sulfuric acid, leads to a slight difference of these oxide layers. The high toxicity of Cr(VI)
compounds, used in the established chromium electroplating process, and the strengthening of
safety and environmental regulations demand a search for substitutes for chromium or at least a
change to less toxic chromium(III) compounds.
Dye and pigment
The mineral crocoite (lead chromate PbCrO4) was used as a yellow pigment shortly after its
discovery. After a synthesis method became available starting from the more abundant
chromite, chrome yellow was, together with cadmium yellow, one of the most used yellow
pigments. The pigment does not photodegrade, but it tends to darken due to the formation of
chromium(III) oxide. It has a strong color, and was used for school buses in the US and for
Postal Service (for example Deutsche Post) in Europe. The use of chrome yellow declined due to
environmental and safety concerns and was replaced by organic pigments or alternatives free
from lead and chromium. Other pigments based on chromium are, for example, the bright red
pigment chrome red, which is a basic lead chromate (PbCrO4·Pb(OH)2). A very important
chromate pigment, which was used widely in metal primer formulations, was zinc chromate, now
replaced by zinc phosphate. A wash primer was formulated to replace the dangerous practice of
pretreating aluminium aircraft bodies with a phosphoric acid solution. This used zinc
tetroxychromate dispersed in a solution of polyvinyl butyral. An 8% solution of phosphoric acid
in solvent was added just before application. It was found that an easily oxidized alcohol was an
essential ingredient. A thin layer of about 10–15 µm was applied, which turned from yellow to
dark green when it was cured. There is still a question as to the correct mechanism. Chrome
green is a mixture of Prussian blue and chrome yellow, while the chrome oxide green
ischromium(III) oxide.
Chromium oxides are also used as a green color in glassmaking and as a glaze in ceramics.
Green chromium oxide is extremely light-fast and as such is used in cladding coatings. It is also
the main ingredient in IR reflecting paints, used by the armed forces, to paint vehicles, to give
them the same IR reflectance as green leaves.
Synthetic ruby and the first laser
Natural rubies are corundum (aluminum oxide) crystals that are colored red (the rarest type) due
to chromium (III) ions (other colors of corundum gems are termed sapphires). A red-colored
artificial ruby may also be achieved by doping chromium(III) into artificial corundum crystals,
thus making chromium a requirement for making synthetic rubies. Such a synthetic ruby crystal
was the basis for the first laser, produced in 1960, which relied on stimulated emission of light
from the chromium atoms in such a crystal.
Wood preservative
Because of their toxicity, chromium(VI) salts are used for the preservation of wood. For
example, chromated copper arsenate (CCA) is used in timber treatment to protect wood from
decay fungi, wood attacking insects, including termites, and marine borers.The formulations
contain chromium based on the oxide CrO3 between 35.3% and 65.5%. In the United States,
65,300 metric tons of CCA solution have been used in 1996. Tanning
Chromium(III) salts, especially chrome alum and chromium(III) sulfate, are used in the tanning
of leather. The chromium(III) stabilizes the leather by cross linking the collagen fibers.
Chromium tanned leather can contain between 4 and 5% of chromium, which is tightly bound to
the proteins. Although the form of chromium used for tanning is not the toxic hexavalent variety,
there remains interest in management of chromium in the tanning industry such as recovery and
reuse, direct/indirect recycling, use of less chromium or "chrome-less" tanning are practiced to
better manage chromium in tanning.
Refractory material
The high heat resistivity and high melting point makes chromite and chromium(III) oxide a
material for high temperature refractory applications, like blast furnaces, cement kilns, molds for
the firing of bricks and as foundry sands for the casting of metals. In these applications, the
refractory materials are made from mixtures of chromite and magnesite. The use is declining
because of the environmental regulations due to the possibility of the formation of
chromium(VI).
Catalyst
Several chromium compounds are used as catalysts for processing hydrocarbons. For example
the Phillips catalysts for the production of polyethylene are mixtures of chromium and silicon
dioxide or mixtures of chromium and titanium and aluminium oxide.] Fe-Cr mixed oxides are
employed as high-temperature catalysts for the water gas shift reaction.] Copper chromite is a
useful hydrogenation catalyst.
Properties of Chromium
Atomic number 24
Atomic mass 51.996 g.mol -1
Electronegativity 1.6
Density 7.19 g.cm-3
at 20°C
Melting point 1907 °C
Boiling point 2672 °C
Vanderwaals radius 0.127 nm
Ionic radius 0.061 nm (+3) ; 0.044 nm (+6)
Isotopes 6
Electronic shell [ Ar ] 3d5 4s
1
Energy of first ionization 651.1 kJ.mol -1
Energy of second ionization 1590.1 kJ.mol -1
Energy of first ionization 2987 kJ.mol -1
Standard potential - 0.71 V (Cr3+
/ Cr )
Discovered by Vaughlin in 1797
MANGANESE
is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as
a free element in nature (often in combination with iron), and in many minerals. Manganese is a
metal with important industrial metal alloy uses, particularly in stainless steels.
Historically, manganese is named for various black minerals (such as pyrolusite) from the same
region of Magnesia in Greece which gave names to similar-sounding magnesium, Mg,
and magnetite, an ore of the element iron, Fe. By the mid-18th century, Swedish chemist Carl
Wilhelm Scheele had used pyrolusite to produce chlorine. Scheele and others were aware that
pyrolusite (now known to bemanganese dioxide) contained a new element, but they were not
able to isolate it. Johan Gottlieb Gahnwas the first to isolate an impure sample of manganese
metal in 1774, by reducing the dioxide withcarbon.
Manganese phosphating is used as a treatment for rust and corrosion prevention on steel.
Depending on their oxidation state, manganese ions have various colors and are used industrially
as pigments. Thepermanganates of alkali and alkaline earth metals are powerful oxidizers.
Manganese dioxide is used as the cathode (electron acceptor) material in zinc-
carbon and alkaline batteries.
In biology, manganese(II) ions function as cofactors for a large variety of enzymes with many
functions. Manganese enzymes are particularly essential in detoxification of superoxide free
radicals in organisms that must deal with elemental oxygen. Manganese also functions in the
oxygen-evolving complex of photosynthetic plants. The element is a required trace mineral for
all known living organisms. In larger amounts, and apparently with far greater activity by
inhalation, manganese can cause a poisoning syndrome in mammals, with neurological damage
which is sometimes irreversible.
The origin of the name manganese is complex. In ancient times, two black minerals
from Magnesia in what is now modern Greece, were both calledmagnes from their place of
origin, but were thought to differ in gender. The male magnes attracted iron, and was the iron ore
we now know as lodestone ormagnetite, and which probably gave us the term magnet. The
female magnes ore did not attract iron, but was used to decolorize glass. This
femininemagnes was later called magnesia, known now in modern times
as pyrolusite or manganese dioxide. Neither this mineral nor manganese itself is magnetic. In the
16th century, manganese dioxide was called manganesum (note the two n's instead of one) by
glassmakers, possibly as a corruption and concatenation of two words, since alchemists and
glassmakers eventually had to differentiate a magnesia negra (the black ore) from magnesia
alba (a white ore, also from Magnesia, also useful in glassmaking). Michele Mercati called
magnesia negra manganesa, and finally the metal isolated from it became known
as manganese (German: Mangan). The name magnesia eventually was then used to refer only to
the white magnesia alba (magnesium oxide), which provided the name magnesium for that free
element, when it was eventually isolated, much later.
Several oxides of manganese, for example manganese dioxide, are abundant in nature, and owing
to their color, these oxides have been used as since the Stone Age. The cave paintings
in Gargas contain manganese as pigments and these cave paintings are 30,000 to 24,000 years
old.
Manganese compounds were used by Egyptian and Roman glassmakers, to either remove color
from glass or add color to it. The use as "glassmakers soap" continued through the Middle
Ages until modern times and is evident in 14th-century glass from Venice.
Because of the use in glassmaking, manganese dioxide was available to alchemists, the first
chemists, and was used for experiments. Ignatius Gottfried Kaim (1770) and Johann
Glauber (17th century) discovered that manganese dioxide could be converted to permanganate,
a useful laboratory reagent. By the mid-18th century, the Swedish chemist Carl Wilhelm
Scheele used manganese dioxide to produce chlorine. First, hydrochloric acid, or a mixture of
dilutesulfuric acid and sodium chloride was made to react with manganese dioxide, later
hydrochloric acid from theLeblanc process was used and the manganese dioxide was recycled by
the Weldon process. The production of chlorine and hypochlorite containing bleaching agents
was a large consumer of manganese ores.
Scheele and other chemists were aware that manganese dioxide contained a new element, but
they were not able to isolate it. Johan Gottlieb Gahn was the first to isolate an impure sample of
manganese metal in 1774, by reducing the dioxide with carbon.
The manganese content of some iron ores used in Greece led to the speculations that the steel
produced from that ore contains inadvertent amounts of manganese, making the Spartan steel
exceptionally hard. Around the beginning of the 19th century, manganese was used in
steelmaking and several patents were granted. In 1816, it was noted that adding manganese to
iron made it harder, without making it any more brittle. In 1837, British academic James
Couper noted an association between heavy exposures to manganese in mines with a form
of Parkinson's disease. In 1912, manganese phosphating electrochemical conversion coatings for
protecting firearms against rust and corrosion were patented in the United States, and have seen
widespread use ever since.
The invention of the Leclanché cell in 1866 and the subsequent improvement of the batteries
containing manganese dioxide as cathodic depolarizerincreased the demand of manganese
dioxide. Until the introduction of the nickel-cadmium battery and lithium-containing batteries,
most batteries contained manganese. The zinc-carbon battery and the alkaline battery normally
use industrially produced manganese dioxide, because natural occurring manganese dioxide
contains impurities. In the 20th century, manganese dioxide has seen wide commercial use as the
chief cathodic material for commercial disposable dry cells and dry batteries of both the standard
(zinc-carbon) and alkaline types.
Steel
Manganese is essential to iron and steel production by virtue of its sulfur-fixing, deoxidizing,
and alloyingproperties. Steelmaking, including its ironmaking component, has accounted for
most manganese demand, presently in the range of 85% to 90% of the total demand.[27]
Among a
variety of other uses, manganese is a key component of low-cost stainless steel formulations.
Small amounts of manganese improve the workability of steel at high temperatures, because it
forms a high-melting sulfide and therefore prevents the formation of a liquid iron sulfide at the
grain boundaries. If the manganese content reaches 4%, the embrittlement of the steel becomes a
dominant feature. The embrittlement decreases at higher manganese concentrations and reaches
an acceptable level at 8%. Steel containing 8 to 15% of manganese can have a high tensile
strength of up to 863 MPa. Steel with 12% manganese was used for British steel helmets. This
steel composition was discovered in 1882 by Robert Hadfield and is still known as Hadfield
steel.
Aluminium alloys
The second large application for manganese is as alloying agent for aluminium. Aluminium with
a manganese content of roughly 1.5% has an increased resistance against corrosion due to the
formation of grains absorbing impurities which would lead to galvanic corrosion.The corrosion-
resistantaluminium alloys 3004 and 3104 with a manganese content of 0.8 to 1.5% are the alloys
used for most of the beverage cans.[34]
Before year 2000, more than 1.6 million tonnes have been
used of those alloys; with a content of 1% manganese, this amount would need 16,000 tonnes of
manganese.
Properties of Manganese
Atomic number 25
Atomic mass 54.9380 g.mol -1
Electronegativity according to Pauling 1.5
Density 7.43 g.cm-3
at 20°C
Melting point 1247 °C
Boiling point 2061 °C
Vanderwaals radius 0.126 nm
Ionic radius 0.08 nm (+2) ; 0.046 nm (+7)
Isotopes 7
Electronic shell [ Ar ] 3d5 4s
2
Energy of first ionization 716 kJ.mol -1
Energy of second ionization 1489 kJ.mol -1
Standard potential - 1.05 V ( Mn2+
/ Mn )
Discovered Johann Gahn in 1774
Technetium
is the chemical element with atomic number 43 and the symbol Tc. It is the lowest atomic
number element without any stable isotopes; every form of it is radioactive, meaning it gives off
atomic particles. Nearly all technetium is produced synthetically, and only minute amounts are
found in nature. Naturally occurring technetium occurs as a spontaneous fission
product in uranium ore or by neutron capture in molybdenum ores. The chemical properties of
this silvery gray, crystalline transition metal are intermediate between rhenium and manganese.
Many of technetium's properties were predicted by Dmitri Mendeleev before the element was
discovered. Mendeleev noted a gap in his periodic table and gave the undiscovered element the
provisional name ekamanganese (Em). In 1937, technetium (specifically the technetium-
97 isotope) became the first predominantly artificial element to be produced, hence its name
(from the Greekτεχνητός, meaning "artificial").
Its short-lived gamma ray-emitting nuclear isomer—technetium-99m—is used in nuclear
medicine for a wide variety of diagnostic tests. Technetium-99 is used as a gamma ray-free
source of beta particles. Long-lived technetium isotopes produced commercially are by-products
of fission of uranium-235 innuclear reactors and are extracted from nuclear fuel rods. Because no
isotope of technetium has a half-life longer than 4.2 million years (technetium-98), its detection
in 1952 in red giants, which are billions of years old, helped bolster the theory that stars can
produce heavier elements.
From the 1860s through 1871, early forms of the periodic table proposed by Dimitri Mendeleev
contained a gap between molybdenum (element 42) and ruthenium (element 44). In 1871,
Mendeleev predicted this missing element would occupy the empty place below manganese and
therefore have similar chemical properties. Mendeleev gave it the provisional
name ekamanganese (from eka-, theSanskrit word for one, because the predicted element was
one place down from the known element manganese.)
Many early researchers, both before and after the periodic table was published, were eager to be
the first to discover and name the missing element; its location in the table suggested that it
should be easier to find than other undiscovered elements. It was first thought to have been found
in platinum ores in 1828 and was given the name polinium, but turned out to be impure iridium.
Then, in 1846, the element ilmenium was claimed to have been discovered, but later was
determined to be impureniobium. This mistake was repeated in 1847 with the "discovery"
of pelopium.
In 1877, the Russian chemist Serge Kern reported discovering the missing element in platinum
ore. Kern named what he thought was the new element davyum (after the noted English chemist
Sir Humphry Davy), but it was eventually determined to be a mixture
of iridium, rhodium and iron. Another candidate,lucium, followed in 1896, but it was determined
to be yttrium. Then in 1908, the Japanese chemistMasataka Ogawa found evidence in the
mineral thorianite, which he thought indicated the presence of element 43. Ogawa named the
element nipponium, after Japan (which is Nippon in Japanese). In 2004, H. K Yoshihara used
"a record of X-ray spectrum of Ogawa's nipponium sample from thorianite [which] was
contained in a photographic plate preserved by his family. The spectrum was read and indicated
the absence of the element 43 and the presence of the element 75 (rhenium)."
German chemists Walter Noddack, Otto Berg, and Ida Tacke reported the discovery of
element 75 and element 43 in 1925, and named element 43 masurium (after Masuria in
eastern Prussia, now in Poland, the region where Walter Noddack's family originated). The
group bombarded columbite with a beam of electrons and deduced element 43 was present by
examining X-ray diffraction spectrograms. Thewavelength of the X-rays produced is related to
the atomic number by a formula derived by Henry Moseley in 1913. The team claimed to detect
a faint X-ray signal at a wavelength produced by element 43. Later experimenters could not
replicate the discovery, and it was dismissed as an error for many years. Still, in 1933, a series of
articles on the discovery of elements quoted the namemasurium for element 43. Debate still
exists as to whether the 1925 team actually did discover element 43.
The discovery of element 43 was finally confirmed in a December 1936 experiment at
the University of Palermo in Sicily conducted by Carlo Perrier and Emilio Segrè. In mid-1936,
Segrè visited the United States, first Columbia University in New York and then the Lawrence
Berkeley National Laboratory in California. He persuaded cyclotron inventor Ernest Lawrence to
let him take back some discarded cyclotron parts that had become radioactive. Lawrence mailed
him a molybdenum foil that had been part of the deflector in the cyclotron.
Segrè enlisted his colleague Perrier to attempt to prove, through comparative chemistry, that the
molybdenum activity was indeed from an element with Z = 43. They succeeded in isolating
the isotopestechnetium-95m and technetium-97. University of Palermo officials wanted them to
name their discovery "panormium", after the Latin name for Palermo, Panormus. In
1947 element 43 was named after the Greek word τεχνητός, meaning "artificial", since it was the
first element to be artificially produced. Segrè returned to Berkeley and met Glenn T. Seaborg.
They isolated the metastable isotope technetium-99m, which is now used in some ten million
medical diagnostic procedures annually.
In 1952, astronomer Paul W. Merrill in California detected the spectral signature of technetium
(in particular, light with wavelength of 403.1 nm, 423.8 nm, 426.2 nm, and 429.7 nm) in light
from S-type red giants. The stars were near the end of their lives, yet were rich in this short-lived
element, meaningnuclear reactions within the stars must be producing it. This evidence was used
to bolster the then-unproven theory that stars are where nucleosynthesis of the heavier elements
occurs. More recently, such observations provided evidence that elements were being formed
by neutron capture in the s-process.
Since its discovery, there have been many searches in terrestrial materials for natural sources of
technetium. In 1962, technetium-99 was isolated and identified in pitchblende from the Belgian
Congo in extremely small quantities (about 0.2 ng/kg); there it originates as a spontaneous
fission product ofuranium-238. There is also evidence that the Oklo natural nuclear fission
reactor produced significant amounts of technetium-99, which has since decayed into ruthenium-
99.
Nuclear medicine and biology
Technetium-99m ("m" indicates that this is a metastable nuclear isomer) is used in radioactive
isotope medical tests, for example as the radioactive part of a radioactive tracer that medical
equipment can detect in the human body. It is well suited to the role because it emits readily
detectable 140 keV gamma rays, and its half-life is 6.01 hours (meaning that about 94% of it
decays to technetium-99 in 24 hours). The chemistry of technetium allows it to be bound to a
variety of non-radioactive compounds. It is the entire compound that determines how it is
metabolized. Therefore a single radioactive isotope can be used for a multitude of diagnostic
tests. There are more than 50 commonly used radiopharmaceuticals based on technetium-99m
for imaging and functional studies of
the brain, myocardium, thyroid, lungs, liver, gallbladder, kidneys, skeleton,blood, and tumors.
The longer-lived isotope technetium-95m, with a half-life of 61 days, is used as a radioactive
tracer to study the movement of technetium in the environment and in plant and animal systems
Industrial and chemical
Technetium-99 decays almost entirely by beta decay, emitting beta particles with consistent low
energies and no accompanying gamma rays. Moreover, its long half-life means that this emission
decreases very slowly with time. It can also be extracted to a high chemical and isotopic purity
from radioactive waste. For these reasons, it is a National Institute of Standards and
Technology (NIST) standard beta emitter, and is therefore used for equipment
calibration. Technetium-99 has also been proposed for use in optoelectronic devices
andnanoscale nuclear batteries.
Like rhenium and palladium, technetium can serve as a catalyst. For some reactions, for example
thedehydrogenation of isopropyl alcohol, it is a far more effective catalyst than either rhenium or
palladium. However, its radioactivity is a major problem in finding safe catalytic applications.
When steel is immersed in water, adding a small concentration (55 ppm) of potassium
pertechnetate(VII) to the water protects the steel from corrosion, even if the temperature is raised
to 250 °C. For this reason, pertechnetate has been used as a possible anodic corrosion inhibitor
for steel, although technetium's radioactivity poses problems which limit this application to self-
contained systems. While (for example)CrO2−
4 can also inhibit corrosion, it requires a concentration ten times as high. In one experiment, a
specimen of carbon steel was kept in an aqueous solution of pertechnetate for 20 years and was
still uncorroded. The mechanism by which pertechnetate prevents corrosion is not well
understood, but seems to involve the reversible formation of a thin surface layer. One theory
holds that the pertechnetate reacts with the steel surface to form a layer of
technetium dioxide which prevents further corrosion; the same effect explains how iron powder
can be used to remove pertechnetate from water. (Activated carbon can also be used for the same
effect.) The effect disappears rapidly if the concentration of pertechnetate falls below the
minimum concentration or if too high a concentration of other ions is added.
As noted, the radioactive nature of technetium (3 MBq per liter at the concentrations required)
makes this corrosion protection impractical in almost all situations. Nevertheless, corrosion
protection by pertechnetate ions was proposed (but never adopted) for use in boiling water
reactors.
Properties of Technetium
Atomic number 43
Atomic mass (99) g.mol -1
Electronegativity according to Pauling 1.9
Density 11.5 g.cm-3
at 20°C
Melting point 2200 oC
Boiling point 4877 oC
Vanderwaals radius 0.128 nm
Isotopes 9
Electronic shell [ Kr ] 4d6 5s
1
Discovered by Carlo Perrier in 1937
NEON
Neon is a chemical element with symbol Ne and atomic number 10. It is in group 18 (noble
gases) of the periodic table. Neon is a colorless, odorless monatomic gas under standard
conditions, with about two-thirds the density of air. It was discovered (along
with krypton and xenon) in 1898 as one of the three residual rare inert elements remaining in dry
air, after nitrogen, oxygen, argon and carbon dioxideare removed. Neon was the second of these
three rare gases to be discovered, and was immediately recognized as a new element from its
bright red emission spectrum. The name neon is derived from the Greek word νέον, neuter
singular form of νέος [neos], meaning new. Neon is chemically inert and forms no uncharged
chemical compounds.
During cosmic nucleogenesis of the elements, large amounts of neon are built up from the alpha-
capture fusion process in stars. Although neon is a very common element in the universe and
solar system (it is fifth in cosmic abundance after hydrogen, helium, oxygen and carbon), it is
very rare on Earth. It composes about 18.2 ppm of air by volume (this is about the same as the
molecular or mole fraction), and a smaller fraction in the crust. The reason for neon's relative
scarcity on Earth and the inner (terrestrial) planets, is that neon forms no compounds to fix it to
solids, and is highly volatile, therefore escaping from the planetesimals under the warmth of the
newly-ignited Sun in the early Solar System. Even the atmosphere of Jupiter is somewhat
depleted of neon, presumably for this reason.
Neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or
in high-voltage discharge tubes or neon advertising signs. The red emission line from neon is
also responsible for the well known red light of helium-neon lasers. Neon is used in a few plasma
tube and refrigerant applications but has few other commercial uses. It is commercially extracted
by thefractional distillation of liquid air. It is considerably more expensive than helium, since air
is its only source.
Neon (Greek νέον (neon), neuter singular form of νέος meaning "new"), was discovered in 1898
by the British chemists Sir William Ramsay (1852–1916) and Morris W. Travers (1872–1961) in
London. Neon was discovered when Ramsay chilled a sample of air until it became a liquid, then
warmed the liquid and captured the gases as they boiled off. The gases nitrogen, oxygen,
and argon had been identified, but the remaining gases were isolated in roughly their order of
abundance, in a six-week period beginning at the end of May 1898. First to be identified
was krypton. The next, after krypton had been removed, was a gas which gave a brilliant red
light under spectroscopic discharge. This gas, identified in June, was named neon, the Greek
analogue of "novum," (new), the name Ramsay's son suggested. The characteristic brilliant red-
orange color that is emitted by gaseous neon when excited electrically was noted immediately;
Travers later wrote, "the blaze of crimson light from the tube told its own story and was a sight
to dwell upon and never forget." Finally, the same team discovered xenon by the same process,
in July.
Neon's scarcity precluded its prompt application for lighting along the lines of Moore tubes,
which usednitrogen and which were commercialized in the early 1900s. After 1902, Georges
Claude's company,Air Liquide, was producing industrial quantities of neon as a byproduct of his
air liquefaction business. In December 1910 Claude demonstrated modern neon lighting based
on a sealed tube of neon. Claude tried briefly to get neon tubes to be used for indoor lighting, due
to their intensity, but failed, as homeowners rejected neon light sources due to their color. Finally
in 1912, Claude's associate began selling neon discharge tubes as advertising signs, where they
were instantly more successful as eye catchers. They were introduced to the U.S. in 1923, when
two large neon signs were bought by a Los Angeles Packard car dealership. The glow and
arresting red color made neon advertising completely different from the competition.[13]
Neon played a role in the basic understanding of the nature of atoms in 1913, when J. J.
Thomson, as part of his exploration into the composition of canal rays, channeled streams of
neon ions through a magnetic and an electric field and measured their deflection by placing a
photographic plate in their path. Thomson observed two separate patches of light on the
photographic plate (see image), which suggested two different parabolas of deflection. Thomson
eventually concluded that some of the atomsin the neon gas were of higher mass than the rest.
Though not understood at the time by Thomson, this was the first discovery
of isotopes of stable atoms. It was made by using a crude version of an instrument we now term
as a mass spectrometer.
Neon is often used in signs and produces an unmistakable bright reddish-orange light. Although
still referred to as "neon", all other colors are generated with the other noble gases or by many
colors of fluorescentlighting.
Neon is used in vacuum tubes, high-voltage indicators, lightning arrestors, wave meter
tubes, television tubes, and helium-neon lasers. Liquefied neon is commercially used as
a cryogenic refrigerant in applications not requiring the lower temperature range attainable with
more extreme liquid helium refrigeration.
Both neon gas and liquid neon are relatively expensive – for small quantities, the price of liquid
neon can be more than 55 times that of liquid helium. The driver for neon's expense is the rarity
of neon, which unlike helium, can only be obtained from air.
The triple point temperature of neon (24.5561 K) is a defining fixed point in the International
Temperature Scale of 1990.
Properties of Neon
Element Classification: Inert (Noble) Gas
Density (g/cc): 1.204 (@ -246°C)
Appearance: colorless, odorless, tasteless gas
Atomic Volume (cc/mol): 16.8
Covalent Radius (pm): 71
Specific Heat (@20°C J/g mol): 1.029
Evaporation Heat (kJ/mol): 1.74
Debye Temperature (K): 63.00
Pauling Negativity Number: 0.0
First Ionizing Energy (kJ/mol): 2079.4
Oxidation States: n/a
Lattice Structure: Face-Centered Cubic
Lattice Constant (Å): 4.430
CAS Registry Number: 7440-01-9
LITHIUM
Lithium (from Greek lithos 'stone') is a chemical element with symbol Li and atomic number 3.
It is a soft, silver-white metal belonging to the alkali metal group of chemical elements.
Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali
metals, lithium is highly reactive and flammable. For this reason, it is typically stored in mineral
oil. When cut open, lithium exhibits a metallic luster, but contact with moist air corrodes the
surface quickly to a dull silvery gray, then black tarnish. Because of its high reactivity, lithium
never occurs freely in nature, and instead, only appears in compounds, which are usually ionic.
Lithium occurs in a number of pegmatitic minerals, but due to its solubility as an ion is present in
ocean water and is commonly obtained from brines and clays. On a commercial scale, lithium is
isolated electrolytically from a mixture of lithium chloride and potassium chloride.
The nuclei of lithium verge on instability, since the two stable lithium isotopes found in nature
have among the lowest binding energies per nucleon of all stable nuclides. Because of its relative
nuclear instability, lithium is less common in the solar system than 25 of the first 32 chemical
elements even though the nuclei are very light in atomic weight. For related reasons, lithium has
important links to nuclear physics. The transmutation of lithium atoms to helium in 1932 was the
first fully man-made nuclear reaction, and lithium-6 deuteride serves as a fusion fuel in staged
thermonuclear weapons.
Lithium and its compounds have several industrial applications, including heat-resistant glass
andceramics, high strength-to-weight alloys used in aircraft, lithium batteries and lithium-ion
batteries. These uses consume more than half of lithium production.
Trace amounts of lithium are present in all organisms. The element serves no apparent vital
biological function, since animals and plants survive in good health without it. Non-vital
functions have not been ruled out. The lithium ion Li+ administered as any of several
lithium salts has proved to be useful as amood-stabilizing drug in the treatment of bipolar
disorder, due to neurological effects of the ion in the human body.
Petalite (LiAlSi4O10) was discovered in 1800 by the Brazilian chemist and statesman José
Bonifácio de Andrada e Silva in a mine on the island of Utö, Sweden. However, it was not until
1817 that Johan August Arfwedson, then working in the laboratory of the chemist Jöns Jakob
Berzelius, detected the presence of a new element while analyzing petalite ore. This element
formed compounds similar to those ofsodium and potassium, though
its carbonate and hydroxide were less soluble in water and more alkaline.Berzelius gave the
alkaline material the name "lithion/lithina", from the Greek word λιθoς (transliterated aslithos,
meaning "stone"), to reflect its discovery in a solid mineral, as opposed to potassium, which had
been discovered in plant ashes, and sodium which was known partly for its high abundance in
animal blood. He named the metal inside the material "lithium".
Arfwedson later showed that this same element was present in the
minerals spodumene and lepidolite. In 1818, Christian Gmelin was the first to observe that
lithium salts give a bright red color to flame. However, both Arfwedson and Gmelin tried and
failed to isolate the pure element from its salts. It was not isolated until 1821, when William
Thomas Brande obtained it by electrolysis of lithium oxide, a process that had previously been
employed by the chemist Sir Humphry Davy to isolate the alkali metals potassium and
sodium. Brande also described some pure salts of lithium, such as the chloride, and, estimating
that lithia (lithium oxide) contained about 55% metal, estimated the atomic weight of lithium to
be around 9.8 g/mol (modern value ~6.94 g/mol). In 1855, larger quantities of lithium were
produced through the electrolysis of lithium chloride by Robert Bunsen andAugustus
Matthiessen. The discovery of this procedure henceforth led to commercial production of
lithium, beginning in 1923, by the German companyMetallgesellschaft AG, which performed an
electrolysis of a liquid mixture of lithium chloride and potassium chloride.
The production and use of lithium underwent several drastic changes in history. The first major
application of lithium was in high-temperature lithium greases for aircraft engines or similar
applications in World War II and shortly after. This use was supported by the fact that lithium-
based soaps have a higher melting point than other alkali soaps, and are less corrosive than
calcium based soaps. The small market for lithium soaps and the lubricating greases based upon
them was supported by several small mining operations mostly in the United States.
The demand for lithium increased dramatically during the Cold War with the production
of nuclear fusion weapons. Both lithium-6 and lithium-7 producetritium when irradiated by
neutrons, and are thus useful for the production of tritium by itself, as well as a form of solid
fusion fuel used inside hydrogen bombs in the form of lithium deuteride. The United States
became the prime producer of lithium in the period between the late 1950s and the mid-1980s.
At the end, the stockpile of lithium was roughly 42,000 tonnes of lithium hydroxide. The
stockpiled lithium was depleted in lithium-6 by 75%, which was enough to affect the
measured atomic weight of lithium in many standardized chemicals, and even the atomic weight
of lithium in some "natural sources" of lithium ion which had been "contaminated" by lithium
salts discharged from isotope separation facilities, which had found its way into ground
water.[30][64]
Lithium was used to decrease the melting temperature of glass and to improve the melting
behavior of aluminium oxide when using the Hall-Héroult process. These two uses dominated
the market until the middle of the 1990s. After the end of the nuclear arms race the demand for
lithium decreased and the sale of Department of Energy stockpiles on the open market further
reduced prices.[64]
But in the mid-1990s, several companies started to extract lithium
from brine which proved to be a less expensive method than underground or even open-pit
mining. Most of the mines closed or shifted their focus to other materials as only the ore from
zoned pegmatites could be mined for a competitive price. For example, the US mines near Kings
Mountain, North Carolina closed before the turn of the 21st century.
The use in lithium ion batteries increased the demand for lithium and became the dominant use
in 2007.With the surge of lithium demand in batteries in the 2000s, new companies have
expanded brine extraction efforts to meet the rising demand
Ceramics and glass
Lithium oxide is a widely used flux for processing silica, reducing the melting
point and viscosity of the material and leading to glazes of improved physical properties
including low coefficients for thermal expansion. Lithium oxides are a component of ovenware.
Worldwide, this is the single largest use for lithium compounds.Lithium carbonate (Li2CO3) is
generally used in this application: upon heating it converts to the oxide
Electrical and electronics
In the later years of the 20th century, owing to its high electrochemical potential, lithium became
an important component of the electrolyte and of one of the electrodes in batteries. A
typical lithium-ion battery can generate approximately 3 volts, compared with 2.1 volts for lead-
acid or 1.5 volts for zinc-carbon cells. Because of its low atomic mass, it also has a high charge-
and power-to-weight ratio. Lithium batteries aredisposable (primary) batteries with lithium or its
compounds as an anode.Lithium batteries are not to be confused with lithium-ion batteries,
which are high energy-density rechargeable batteries. Other rechargeable batteries include
the lithium-ion polymer battery, lithium iron phosphate battery, and the nano wire battery.
Properties of Lithium
Atomic number 3
Atomic mass 6.941 g.mol -1
Electronegativity according to Pauling 1.0
Density 0.53 g.cm -3
at 20 °C
Melting point 180.5 °C
Boiling point 1342 °C
Vanderwaals radius 0.145 nm
Ionic radius 0.06 nm
Isotopes 2
Electronic shell 1s22s
1 or [He] 2s
1
Energy of first ionization 520.1 kJ.mol -1
Standard potential- 3.02 V
Discovered by Johann Arfvedson in 1817
MERCURY
Mercury is a chemical element with the symbol Hg and atomic number 80. It is commonly
known asquicksilver and was formerly named hydrargyrum (from Greek "hydr-" water and
"argyros" silver). A heavy, silvery d-block element, mercury is the only metal that is liquid
at standard conditions for temperature and pressure; the only other element that is liquid under
these conditions is bromine, though metals such as caesium, gallium, and rubidium melt just
above room temperature. With a freezing pointof −38.83 °C and boiling point of 356.73 °C,
mercury has one of the narrowest ranges of its liquid state of any metal.
Mercury occurs in deposits throughout the world mostly as cinnabar (mercuric sulfide). The red
pigmentvermilion, a pure form of mercuric sulfide, is mostly obtained by reaction of mercury
(produced by reduction from cinnabar) with sulfur. Cinnabar is highly toxic by ingestion or
inhalation of the dust.Mercury poisoning can also result from exposure to water-soluble forms of
mercury (such as mercuric chloride or methylmercury), inhalation of mercury vapor, or eating
seafood contaminated with mercury.
Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float
valves, mercury switches, mercury relays, fluorescent lamps and other devices though concerns
about the element's toxicity have led to mercury thermometers and sphygmomanometers being
largely phased out in clinical environments in favour of alcohol or galinstan-filled glass
thermometers alternatively thermistor orinfrared-based electronic instruments, mechanical
pressure gauges and electronic strain gauge sensors have replaced mercury sphygmomanometers.
It remains in use in scientific research applications and inamalgam material for dental
restoration in some locales. It is used in lighting: electricity passed through mercury vapor in a
fluorescent lamp produces short-wave ultraviolet light which then causes the phosphor in the
tube to fluoresce, making visible light.
Mercury was found in Egyptian tombs that date from 1500 BC.
In China and Tibet, mercury use was thought to prolong life, heal fractures, and maintain
generally good health, although it is now known that exposure to mercury leads to serious
adverse health effects. The first emperor of China, Qín Shǐ Huáng Dì — allegedly buried in a
tomb that contained rivers of flowing mercury on a model of the land he ruled, representative of
the rivers of China — was killed by drinking a mercury and powdered jade mixture formulated
by Qin alchemists (causing liver failure,mercury poisoning, and brain death) who intended to
give him eternal life.
The ancient Greeks used mercury in ointments; the ancient Egyptians and the Romans used it
in cosmetics which sometimes deformed the face. In Lamanai, once a major city of the Maya
civilization, a pool of mercury was found under a marker in aMesoamerican ballcourt. By 500
BC mercury was used to make amalgams (Medieval Latin amalgama, "alloy of mercury") with
other metals.
Alchemists thought of mercury as the First Matter from which all metals were formed. They
believed that different metals could be produced by varying the quality and quantity
of sulfur contained within the mercury. The purest of these was gold, and mercury was called for
in attempts at the transmutation of base (or impure) metals into gold, which was the goal of many
alchemists.
Hg is the modern chemical symbol for mercury. It comes from hydrargyrum, a Latinized form of
the Greek word Ύδραργσρος (hydrargyros), which is a compound word meaning "water-silver"
(hydr- = water, argyros = silver) — since it is liquid like water and shiny like silver. The element
was named after the Roman god Mercury, known for speed and mobility. It is associated with the
planet Mercury; the astrological symbol for the planet is also one of thealchemical symbols for
the metal; the Sanskrit word for alchemy is Rasavātam which means "the way of
mercury". Mercury is the only metal for which the alchemical planetary name became the
common name.
The mines in Almadén (Spain), Monte Amiata (Italy), and Idrija (now Slovenia) dominated
mercury production from the opening of the mine in Almadén 2500 years ago, until new deposits
were found at the end of the 19th century.
Production of chlorine and caustic soda
Chlorine is produced from sodium chloride (common salt, NaCl) using electrolysis to separate
the metallicsodium from the chlorine gas. Usually the salt is dissolved in water to produce a
brine. By-products of any suchchloralkali process are hydrogen (H2) and sodium
hydroxide (NaOH), which is commonly called caustic soda orlye. By far the largest use of
mercury in the late 20th century was in the mercury cell process (also called theCastner-Kellner
process) where metallic sodium is formed as an amalgam at a cathode made from mercury; this
sodium is then reacted with water to produce sodium hydroxide. Many of the industrial mercury
releases of the 20th century came from this process, although modern plants claimed to be safe in
this regard After about 1985, all new chloralkali production facilities that were built in the
United States used either membrane cell or diaphragm cell technologies to produce chlorine.
Laboratory uses
Some medical thermometers, especially those for high temperatures, are filled with mercury;
however, they are gradually disappearing. In the United States, non-prescription sale of mercury
fever thermometers has been banned since 2003.[51]
Mercury is also found in liquid mirror telescopes.
Some transit telescopes use a basin of mercury to form a flat and absolutely horizontal mirror,
useful in determining an absolute vertical or perpendicular reference. Concave horizontal
parabolic mirrors may be formed by rotating liquid mercury on a disk, the parabolic form of the
liquid thus formed reflecting and focusing incident light. Such telescopes are cheaper than
conventional large mirror telescopes by up to a factor of 100, but the mirror cannot be tilted and
always points straight up.
Liquid mercury is a part of popular secondary reference electrode (called the calomel electrode)
in electrochemistry as an alternative to the standard hydrogen electrode. The calomel electrode is
used to work out the electrode potential of half cells. Last, but not least, the triple point of
mercury, −38.8344 °C, is a fixed point used as a temperature standard for the International
Temperature Scale (ITS-90)
Properties of Mercury
Atomic number 80
Atomic mass 200.59 g.mol -1
Electronegativity according to Pauling 1.9
Density 13.6 g.cm-3
at 20°C
Melting point - 38.9 °C
Boiling point 356.6 °C
Vanderwaals radius 0.157 nm
Ionic radius 0.11 nm (+2)
Isotopes 12
Electronic shell [ Xe ] 4f14
5d10
6s2
Energy of first ionization 1004.6 kJ.mol -1
Energy of second ionization 1796 kJ.mol -1
Energy of third ionization 3294 kJ.mol -1
Standard potential + 0.854 V ( Hg2+
/ Hg )
Discovered by The ancients
Astatine
Astatine is a radioactive chemical element with the chemical symbol At and atomic number 85.
It occurs on Earth only as the result of the radioactive decay of certain heavier elements. All of
its isotopesare short-lived; the most stable is astatine-210, with a half-life of 8.1 hours.
Accordingly, much less is known about astatine than most other elements. The observed
properties are consistent with it being a heavier analog of iodine; many other properties have
been estimated based on this resemblance.
Elemental astatine has never been viewed, because a mass large enough to be seen (by the naked
human eye) would be immediately vaporized by the heat generated by its own radioactivity.
Astatine may be dark, or it may have a metallic appearance and be a semiconductor, or it may
even be a metal. It is likely to have a much higher melting point than iodine, on par with those
of bismuth and polonium. Chemically, astatine behaves more or less as a halogen (the group
including chlorine and fluorine), being expected to form ionic astatides with alkali or alkaline
earth metals; it is known to form covalent compounds with nonmetals, including other halogens.
It does, however, also have a notable cationic chemistry that distinguishes it from the lighter
halogens. The second longest-lived isotope of astatine, astatine-211, is the only one currently
having any commercial application, being employed in medicine to diagnose and treat some
diseases via its emission of alpha particles (helium-4 nuclei). Only extremely small quantities are
used, however, due to its intense radioactivity.
The element was first produced by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio
Segrè at theUniversity of California, Berkeley in 1940. They named the element "astatine", a
name coming from the great instability of the synthesized matter (the source Greek word
αστατος (astatos) means "unstable"). Three years later it was found in nature, although it is the
least abundant element in the Earth's crust among the non-transuranic elements, with a total
existing amount of much less than one gram at any given time. Six astatine isotopes, with mass
numbers of 214 to 219, are present in nature as the products of various decay routes of heavier
elements, but neither the most stable isotope of astatine (with mass number 210) nor astatine-211
(which is used in medicine) is produced naturally.
In 1869, when Dmitri Mendeleev published his periodic table, the space under iodine was empty;
after Niels Bohr established the physical basis of the classification of chemical elements, it was
suggested that the fifth halogen belonged there. Before its officially recognized discovery, it was
called "eka-iodine" (from Sanskrit eka – "one") to imply it was one space under iodine (in the
same manner as eka-silicon, eka-boron, and others). Scientists tried to find it in nature; given its
rarity, these attempts resulted in a number of false discoveries.
The first claimed discovery of eka-iodine was made by Fred Allison and his associates at the
Alabama Polytechnic Institute (now Auburn University) in 1931. The discoverers named element
85 "alabamine", and assigned it the symbol Ab, designations that were used for a few years
afterward. In 1934, however, H. G. MacPherson of University of California, Berkeley disproved
Allison's method and the validity of his discovery.[62]
This erroneous discovery was followed by
another claim in 1937, by the chemist Rajendralal De. Working inDacca in British
India (now Dhaka in Bangladesh), he chose the name "dakin" for element 85, which he claimed
to have isolated as the thorium seriesequivalent of Radium F (polonium-210) in the radium
series. The properties he reported for dakin do not correspond to those of astatine, and the true
identity of dakin is not known.
In 1940, the Swiss chemist Walter Minder announced the discovery of element 85 as the beta
decay product of Radium A (polonium-218), choosing the name "helvetium" (from Helvetia,
"Switzerland"). However, Berta Karlik and Traude Bernert were unsuccessful in reproducing his
experiments, and subsequently attributed Minder's results to contamination of his radon stream
(radon-222 is the parent isotope of polonium-218). In 1942, Minder, in collaboration with the
English scientist Alice Leigh-Smith, announced the discovery of another isotope of element 85,
presumed to be the product of Thorium A (polonium-216) beta decay. They named this
substance "anglo-helvetium",[65]
but Karlik and Bernert were again unable to reproduce these
results.
In 1940, Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè finally isolated the
element at the University of California, Berkeley. Instead of searching for the element in nature,
the scientists created it by bombarding bismuth-209with alpha particles in a cyclotron (particle
accelerator) to produce, after emission of two neutrons, astatine-211. The name "astatine" comes
from the Greek word αστατος (astatos, meaning "unstable"), due to its propensity for radioactive
decay (later, all isotopes of the element were shown to be unstable), together with the ending "-
ine", found in the names of the four previously discovered halogens. Three years later, astatine
was found as a product of naturally occurring decay chains by Karlik and Bernert. Since then,
astatine has been determined to be in three out of the four natural decay chains.
Astatine is an extremely radioactive element; all its isotopes have half-lives of less than 12 hours,
decaying into bismuth, polonium, radon, or other astatine isotopes. Among the first 101 elements
in the periodic table, only francium is less stable.[3]
The bulk properties of astatine are not known with any great degree of certainty. Research is
limited by its short half-life, which prevents the creation of weighable quantities. A visible piece
of astatine would be immediately and completely vaporized due to the heat generated by its
intense radioactivity. Astatine is usually classified as either a nonmetal or a metalloid. However,
metal formation for condensed-phase astatine has also been suggested
Properties of Astatine
Atomic number 85
Atomic mass (210) g.mol -1
Electronegativity according to Pauling 2.2
Density unknown
Melting point 302 °C
Boiling point 337 °C (estimation)
Vanderwaals radius unknown
Ionic radius unknown
Isotopes 7
Electronic shell [ Xe ] 4f14 5d10 6s2 6p5
Energy of first ionization (926) kJ.mol -1
Discovered by D.R. Corson 1940
Molybdenum
Molybdenum is a Group 6 chemical element with the symbol Mo and atomic number 42. The
name is from Neo-Latin Molybdaenum, from Ancient Greek Μόλσβδος molybdos, meaning lead,
since its ores were confused with lead ores. Molybdenum minerals have been known into
prehistory, but the element was discovered (in the sense of differentiating it as a new entity from
the mineral salts of other metals) in 1778 by Carl Wilhelm Scheele. The metal was first isolated
in 1781 by Peter Jacob Hjelm.
Molybdenum does not occur naturally as a free metal on Earth, but rather in various oxidation
states in minerals. The free element, which is a silvery metal with a gray cast, has the sixth-
highest melting pointof any element. It readily forms hard, stable carbides in alloys, and for this
reason most of world production of the element (about 80%) is in making many types
of steel alloys, including high strength alloys and superalloys.
Most molybdenum compounds have low solubility in water, but the molybdate ion MoO42−
is
soluble and forms when molybdenum-containing minerals are in contact with oxygen and water.
Industrially, molybdenum compounds (about 14% of world production of the element) are used
in high-pressure and high-temperature applications, as pigments and catalysts.
Molybdenum-containing enzymes are by far the most common catalysts used by some bacteria
to break the chemical bond in atmospheric molecular nitrogen, allowing biological nitrogen
fixation. At least 50 molybdenum-containing enzymes are now known in bacteria and animals,
although only bacterial and cyanobacterial enzymes are involved in nitrogen fixation, and
these nitrogenases contain molybdenum in a different form from the rest. Owing to the diverse
functions of the various other types of molybdenum enzymes, molybdenum is a required element
for life in all higher organisms (eukaryotes), though not in all bacteria.
Molybdenite—the principal ore from which molybdenum is now extracted—was previously
known as molybdena. Molybdena was confused with and often utilized as though it
were graphite. Like graphite, molybdenite can be used to blacken a surface or as a solid
lubricant.Even when molybdena was distinguishable from graphite, it was still confused with the
common lead ore PbS (now called galena); the name comes from Ancient
Greek Μόλσβδος molybdos, meaning lead. (The Greek word itself has been proposed as
aloanword from Anatolian Luvian and Lydian languages)
Although apparent deliberate alloying of molybdenum with steel in one 14th-century Japanese
sword (mfd. ca. 1330) has been reported, that art was never employed widely and was later
lost. In the West in 1754, Bengt Andersson Qvist examined molybdenite and determined that it
did not contain lead, and thus was not the same as galena.
By 1778 Swedish chemist Carl Wilhelm Scheele stated firmly that molybdena was (indeed) not
galena nor graphite. Instead, Scheele went further and correctly proposed that molybdena was an
ore of a distinct new element, named molybdenum for the mineral in which it resided, and from
which it might be isolated. Peter Jacob Hjelm successfully isolated molybdenum by
using carbon and linseed oil in 1781.
For about a century after its isolation, molybdenum had no industrial use, owing to its relative
scarcity, difficulty extracting the pure metal, and the immaturity of appropriate metallurgical
techniques. Early molybdenum steel alloys showed great promise in their increased hardness, but
efforts to manufacture them on a large scale were hampered by inconsistent results and a
tendency toward brittleness and recrystallization. In 1906, William D. Coolidge filed a patent for
rendering molybdenum ductile, leading to its use as a heating element for high-temperature
furnaces and as a support for tungsten-filament light bulbs; oxide formation and degradation
require that molybdenum be physically sealed or held in an inert gas. In 1913, Frank E.
Elmore developed a flotation processto recover molybdenite from ores; flotation remains the
primary isolation process
During the first World War, demand for molybdenum spiked; it was used both in armor
plating and as a substitute for tungsten in high speed steels. Some British tanks were protected by
75 mm (3 in) manganese steel plating, but this proved to be ineffective. The manganese steel
plates were replaced with 25 mm (1 in) molybdenum-steel plating allowing for higher speed,
greater maneuverability, and better protection. The Germans also used molybdenum-
doped steel for heavy artillery. This was because traditional steel melted at the heat produced by
enough gunpowder to launch a one ton shell. After the war, demand plummeted until
metallurgical advances allowed extensive development of peacetime applications. In World War
II, molybdenum again saw strategic importance as a substitute for tungsten in steel alloys
Properties of Molybdenum
Atomic number 42
Atomic mass 95.94 g.mol -1
Electronegativity according to Pauling 1.8
Density 10.2 g.cm-3
at 20°C
Melting point 2610 °C
Boiling point 4825 °C
Vanderwaals radius 0.139 nm
Ionic radius 0.068 nm (+4) ; 0.06 nm (+6)
Isotopes 11
Electronic shell [ Kr ] 4d5 5s
1
Energy of first ionization 651 kJ.mol -1
Standard potential - 0.2 V
Discovered by Carl Wilhelm Scheele in 1778
LANTHANUM
Lanthanum is a chemical element with the symbol La and atomic number 57. Lanthanum is a
silvery white metallic element that belongs to group 3 of the periodic table and is the first
element of thelanthanide series. It is found in some rare-earth minerals, usually in combination
with cerium and otherrare earth elements. Lanthanum is a malleable, ductile, and soft metal that
oxidizes rapidly when exposed to air. It is produced from the
minerals monazite and bastnäsite using a complex multistage extraction process. Lanthanum
compounds have numerous applications as catalysts, additives in glass, carbon lighting for studio
lighting and projection, ignition elements in lighters and torches, electron cathodes, scintillators,
and others. Lanthanum carbonate (La2(CO3)3) was approved as a medication against renal
failure.
The word lanthanum comes from the Greek λανθανω [lanthanō] = to lie hidden. Lanthanum was
discovered in 1839 by Swedish chemist Carl Gustav Mosander, when he partially decomposed a
sample of cerium nitrate by heating and treating the resulting salt with dilute nitric acid. From
the resulting solution, he isolated a new rare earth he called lantana. Lanthanum was isolated in
relatively pure form in 1923.
Lanthanum is the most strongly basic of all the trivalent lanthanides, and this property is what
allowed Mosander to isolate and purify the salts of this element. Basicity separation as operated
commercially involved the fractional precipitation of the weaker bases (such as didymium) from
nitrate solution by the addition of magnesium oxide or dilute ammonia gas. Purified lanthanum
remained in solution. (The basicity methods were only suitable for lanthanum purification;
didymium could not be efficiently further separated in this manner.) The alternative technique of
fractional crystallization was invented by Dmitri Mendeleev, in the form of the double
ammonium nitrate tetrahydrate, which he used to separate the less-soluble lanthanum from the
more-soluble didymium in the 1870s. This system was used commercially in lanthanum
purification until the development of practical solvent extraction methods that started in the late
1950s. (A detailed process using the double ammonium nitrates to provide 99.99% pure
lanthanum, neodymium concentrates and praseodymium concentrates is presented in Callow
1967, at a time when the process was just becoming obsolete.) As operated for lanthanum
purification, the double ammonium nitrates were recrystallized from water. When later adapted
by Carl Auer von Welsbach for the splitting of didymium, nitric acid was used as a solvent to
lower the solubility of the system. Lanthanum is relatively easy to purify, since it has only one
adjacent lanthanide, cerium, which itself is very readily removed due to its potential tetravalency.
The fractional crystallization purification of lanthanum as the double ammonium nitrate was
sufficiently rapid and efficient, that lanthanum purified in this manner was not expensive. The
Lindsay Chemical Division of American Potash and Chemical Corporation, for a while the
largest producer of rare earths in the world, in a price list dated October 1, 1958 priced 99.9%
lanthanum ammonium nitrate (oxide content of 29%) at $3.15 per pound, or $1.93 per pound in
50-pound quantities. The corresponding oxide (slightly purer at 99.99%) was priced at $11.70 or
$7.15 per pound for the two quantity ranges. The price for their purest grade of oxide (99.997%)
was $21.60 and $13.20, respectively
One material used for anodic material of nickel-metal hydride batteries is
La(Ni3.6Mn0.4Al0.3Co0.7. Due to high cost to extract the other lanthanides a mischmetal with
more than 50% of lanthanum is used instead of pure lanthanum. The compound is
an intermetallic component of the AB5 type.
As most hybrid cars use nickel-metal hydride batteries, massive quantities of lanthanum are
required for the production of hybrid automobiles. A typical hybrid automobile battery for
a Toyota Prius requires 10 to 15 kg (22-33 lb) of lanthanum. As engineers push the technology to
increase fuel mileage, twice that amount of lanthanum could be required per vehicle.
Hydrogen sponge alloys can contain lanthanum. These alloys are capable of storing up to
400 times their own volume of hydrogen gas in a reversible adsorption process. Heat energy
is released every time they do so; therefore these alloys have possibilities in energy
conservation systems.
Mischmetal, a pyrophoric alloy used in lighter flints, contains 25% to 45% lanthanum.[2]
Lanthanum oxide and the boride are used in electronic vacuum tubes as hot
cathode materials with strong emissivity of electrons. Crystals of LaB6 are used in high
brightness, extended life, thermionic electron emission sources for electron
microscopes and Hall effect thrusters.
Lanthanum fluoride (LaF3) is an essential component of a heavy fluoride glass
named ZBLAN. This glass has superior transmittance in the infrared range and is therefore
used for fiber-optical communication systems.
Cerium doped lanthanum bromide and lanthanum chloride are the recent
inorganic scintillators which have a combination of high light yield, best energy resolution
and fast response. Their high yield converts into superior energy resolution; moreover, the
light output is very stable and quite high over a very wide range of temperatures, making it
particularly attractive for high temperature applications. These scintillators are already
widely used commercially in detectors of neutrons or gamma rays.
Carbon arc lamps use a mixture of rare earth elements to improve the light quality. This
application, especially by the motion picture industry for studio lighting and projection,
consumed about 25% of the rare-earth compounds produced until the phase out of Carbon
arc lamps.
Lanthanum(III) oxide (La2O3) improves the alkali resistance of glass, and is used in making
special optical glasses, such as infrared-absorbing glass, as well
as camera and telescope lenses, because of the highrefractive index and low dispersion of
rare-earth glasses. Lanthanum oxide is also used as a grain growth additive during the liquid
phase sintering of silicon nitride and zirconium diboride.
Small amounts of lanthanum added to steel improves its malleability, resistance to impact
and ductility. Whereas addition of lanthanum to molybdenum decreases its hardness and
sensitivity to temperature variations.
Small amounts of lanthanum are present in many pool products to remove the phosphates
that feed algae.
Properties of LANTHANUM
Atomic number 57
Atomic mass 138.91 g.mol -1
Electronegativity according to Pauling 1.1
Density 6.18 g.cm-3
at 20°C
Melting point 826 °C
Boiling point 0.186 nm
Vanderwaals radius 0.104 nm (+3)
Isotopes 7
Electronic shell [ Xe ] 5d1 6s
2
Energy of first ionization 539 kJ.mol -1
Energy of second ionization 1098 kJ.mol -1
Energy of third ionization 1840 kJ.mol -1
Standard potential - 2.52 V ( La+3
/ La )
Discovered by Carl Mosander in 1839
Tin
Tin is a chemical element with symbol Sn (for Latin: stannum) and atomic number 50. It is
a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both
neighboring group-14 elements, germanium and lead, and has two possible oxidation states, +2
and the slightly more stable +4. Tin is the 49th most abundant element and has, with 10 stable
isotopes, the largest number of stableisotopes in the periodic table. Tin is obtained chiefly from
the mineral cassiterite, where it occurs as tin dioxide, SnO2.
This silvery, malleable poor metal is not easily oxidized in air and is used to coat other metals to
preventcorrosion. The first alloy, used in large scale since 3000 BC, was bronze, an alloy of tin
and copper. After 600 BC pure metallic tin was produced. Pewter, which is an alloy of 85–90%
tin with the remainder commonly consisting of copper, antimony and lead, was used
for flatware from the Bronze Age until the 20th century. In modern times tin is used in many
alloys, most notably tin/lead soft solders, typically containing 60% or more of tin. Another large
application for tin is corrosion-resistant tin plating of steel. Because of its low toxicity, tin-plated
metal is also used for food packaging, giving the name to tin cans, which are made mostly of
steel.
Tin extraction and use can be dated to the beginnings of the Bronze Age around 3000 BC, when
it was observed that copper objects formed of polymetallic ores with different metal contents had
different physical properties. The earliest bronze objects had tin or arsenic content of less than
2% and are therefore believed to be the result of unintentional alloying due to trace metal content
in the copper ore. The addition of a second metal to copper increases its hardness, lowers the
melting temperature, and improves thecasting process by producing a more fluid melt that cools
to a denser, less spongy metal. This was an important innovation that allowed for the much more
complex shapes cast in closed moulds of the Bronze Age. Arsenical bronze objects appear first in
the Near East where arsenic is commonly found in association with copper ore, but the health
risks were quickly realized and the quest for sources of the much less hazardous tin ores began
early in the Bronze Age. This created the demand for rare tin metal and formed a trade network
that linked the distant sources of tin to the markets of Bronze Age cultures.
Cassiterite (SnO2), the tin oxide form of tin, was most likely the original source of tin in ancient
times. Other forms of tin ores are less abundant sulfides such as stannite that require a more
involved smelting process. Cassiterite often accumulates in alluvial channels as placer
deposits due to the fact that it is harder, heavier, and more chemically resistant than the granite in
which it typically forms. These deposits can be easily seen in river banks as cassiterite is usually
black, purple or otherwise dark in color, a feature exploited by early Bronze Age prospectors. It
is likely that the earliest deposits were alluvial in nature, and perhaps exploited by the same
methods used for panninggold in placer deposits.
Solder
Tin has long been used as a solder in the form of an alloy with lead, tin accounting for 5 to 70%
w/w. Tin forms a eutectic mixture with lead containing 63% tin and 37% lead. Such solders are
primarily used for solders for joining pipes or electric circuits. Since the European Union Waste
Electrical and Electronic Equipment Directive (WEEE Directive) and Restriction of Hazardous
Substances Directive came into effect on 1 July 2006, the use of lead in such alloys has
decreased. Replacing lead has many problems, including a higher melting point, and the and the
formation of tin whiskers causing electrical problems.
Tin pest can occur in lead-free solders, leading to loss of the soldered joint. Replacement alloys
are rapidly being found, although problems of joint integrity remain.
Properties of Tin
Atomic number 50
Atomic mass 118.69 g.mol -1
Electronegativity according to Pauling 1.8
Density 5.77g.cm-3
(alpha) and 7.3 g.cm-3
at 20°C (beta)
Melting point 232 °C
Boiling point 2270 °C
Vanderwaals radius 0.162 nm
Ionic radius 0.112 nm (+2) ; 0.070 nm (+4)
Isotopes 20
Electronic shell [ Kr ] 4d10
5s25p
2
Energy of first ionization 708.4 kJ.mol -1
Energy of second ionization 1411.4 kJ.mol -1
Energy of third ionization 2942.2 kJ.mol -1
Energy of fourth ionization 3929.3 kJ.mol -1
Discovered by The ancients
Protactinum
Protactinium is a chemical element with the symbol Pa and atomic number 91. It is a dense,
silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms
various chemical compounds where protactinium is usually present in the oxidation state +5, but
can also assume +4 and even +2 or +3 states. The average concentrations of protactinium in the
Earth's crust is typically on the order of a few parts per trillion, but may reach up to a few parts
per million in some uraninite ore deposits. Because of its scarcity, high radioactivity and high
toxicity, there are currently no uses for protactinium outside of scientific research, and for this
purpose, protactinium is mostly extracted from spent nuclear fuel.
Protactinium was first identified in 1913 by Kasimir Fajans and Oswald Helmuth Göhring and
namedbrevium because of the short half-life of the specific isotope studied, namely protactinium-
234. A more stable isotope (231
Pa) of protactinium was discovered in 1917/18 by Otto
Hahn and Lise Meitner, and they chose the name proto-actinium, but then the IUPAC named it
finally protactinium in 1949 and confirmed Hahn and Meitner as discoverers. The new name
meant "parent of actinium" and reflected the fact that actinium is a product of radioactive decay
of protactinium.
The longest-lived and most abundant (nearly 100%) naturally occurring isotope of protactinium,
protactinium-231, has a half-life of 32,760 years and is a decay product of uranium-235. Much
smaller trace amounts of the short-lived nuclear isomer protactinium-234m occur in the decay
chain of uranium-238. Protactinium-233 results from the decay of thorium-233 as part of the
chain of events used to produce uranium-233 by neutron irradiation of thorium-232. It is an
undesired intermediate product in thorium-based nuclear reactors and is therefore removed from
the active zone of the reactor during the breeding process. Analysis of the relative concentrations
of various uranium, thorium and protactinium isotopes in water and minerals is used
in radiometric dating of sediments which are up to 175,000 years old and in modeling of various
geological processes.
In 1871, Dmitri Mendeleev predicted the existence of an element
between thorium and uranium. The actinide element group was unknown at the time. Therefore,
uranium was positioned below tungsten, and thorium below zirconium, leaving the space below
tantalum empty and, until the 1950s, periodic tables were published with this structure. For a
long time chemists searched for eka-tantalum as an element with similar chemical properties as
tantalum, making a discovery of protactinium nearly impossible.
In 1900, William Crookes isolated protactinium as an intensely radioactive material from
uranium; however, he could not characterize it as a new chemical element and thus named it
uranium-X. Crookes dissolved uranium nitrate in ether, the residual aqueous phase contains most
of the 234
90Thand 234
91Pa. His method was still used in the 1950s to isolate 234
90Th and 234
91Pa from uranium compounds.[6]
Protactinium was first identified in 1913, when Kasimir
Fajans and Oswald Helmuth Göhring encountered the isotope 234
Pa during their studies of the
decay chains of uranium-238: 238
92U→ 234
90Th → 234
91Pa → 234
92U. They named the new element brevium (from the Latin word, brevis, meaning brief or short)
because of its short half-life, 6.7 hours for 234
91Pa. In 1917/18, two groups of scientists, Otto Hahn and Lise
Meitner of Germany and Frederick Soddy and John Cranston of Great Britain, independently
discovered another isotope of protactinium, 231
Pa having much longer half-life of about
32,000 years. Thus the name brevium was changed to protoactinium as the new element was part
of the decay chain of uranium-235 before the actinium
(from Greek: πρῶτος = protosmeaning first, before). For ease of pronunciation, the name was
shortened to protactinium by theIUPAC in 1949. The discovery of protactinium completed the
last gap in the early versions of the periodic table, proposed by Mendeleev in 1869, and it
brought to fame the involved scientists.
Aristid von Grosse produced 2 milligrams of Pa2O5 in 1927, and in 1934 first isolated elemental
protactinium from 0.1 milligrams of Pa2O5. He used two different procedures: in the first one,
protactinium oxide was irradiated by 35 keV electrons in vacuum. In another method, called
the van Arkel–de Boer process, the oxide was chemically converted to
a halide (chloride, bromide or iodide) and then reduced in a vacuum with an electrically heated
metallic filament:
2 PaI5 → 2 Pa + 5 I2
In 1961, the British Atomic Energy Authority (UKAEA) produced 125 grams of 99.9% pure
protactinium by processing 60 tonnes of waste material in a 12-stage process, at a cost of about
500,000 USD. For many years, this was the world's only significant supply of protactinium,
which was provided to various laboratories for scientific studies. Oak Ridge National
Laboratory in the US is currently providing protactinium at a cost of about 280 USD/gram.
Although protactinium is located in the periodic table between uranium and thorium, which both
have numerous applications, owing to its scarcity, high radioactivity and high toxicity, there are
currently no uses for protactinium outside of scientific research.
Protactinium-231 arises from the decay of uranium-235 formed in nuclear reactors, and by the
reaction 232
Th + n → 231
Th + 2n and subsequent beta decay. It may support a nuclear chain
reaction, which could in principle be used to build nuclear weapons. The physicist Walter
Seifritz once estimated the associated critical mass as 750±180 kg,but this possibility (of a chain
reaction) has been ruled out by other nuclear physicists since then.
With the advent of highly sensitive mass spectrometers, an application of 231
Pa as a tracer in
geology and paleoceanography has become possible. So, the ratio of protactinium-231 to
thorium-230 is used for radiometric dating of sediments which are up to 175,000 years old and in
modeling of the formation of minerals. In particular, its evaluation in oceanic sediments allowed
to reconstruct the movements of North Atlantic water bodies during the last melting of Ice
Age glaciers. Some of the protactinium-related dating variations rely on the analysis of the
relative concentrations for several long-living members of the uranium decay chain – uranium,
thorium and protactinium, for example. These elements have 6, 5 and 4 f-electrons in the outer
shell and thus favor +6, +5 and +4 oxidation states, respectively, and show different physical and
chemical properties. So, thorium and protactinium, but not uranium compounds are poorly
soluble in aqueous solutions, and precipitate into sediments; the precipitation rate is faster for
thorium than for protactinium. Besides, the concentration analysis for both protactinium-231
(half-life 32,750 years) and thorium-230 (half-life 75,380 years) allows to improve the accuracy
compared to when only one isotope is measured; this double-isotope method is also weakly
sensitive to inhomogeneities in the spatial distribution of the isotopes and to variations in their
precipitation rate.
Properties of Protactinum
Atomic number 91
Atomic mass 231.0359 g.mol -1
Electronegativity according to Pauling 1.5
Density 15.37 g.cm-3
at 20°C
Melting point 1600 °C
Boiling point unknown
Vanderwaals radius unknown
Ionic radius unknown
Isotopes 5
Electronic shell [ Rn ] 5f2 6d
1 7s
2
Discovered by K. Kajans and O.H. Gohring in 1913
FLOURINE
Fluorine is the chemical element with symbol F and atomic number 9. The lightest halogen, it
has a single stable isotope, fluorine-19. At standard pressure and temperature, the element is a
pale yellow gas composed of diatomic molecules, F2. Fluorine is the
most electronegative element and also the most reactive, requiring great care in
handling. Compounds of fluorine are called fluorides.
In stars, fluorine is rare, for a light element, because it is consumed in fusion reactions. Within
Earth's crust, fluorine is the thirteenth-most abundant element. The most important fluorine
mineral, fluorite, was first formally described in 1529. The mineral's name derived from the
Latin verb fluo, meaning "flow", because it was added to metal ores to lower their melting
points. Suggested as a chemical element in 1811, the dangerous element injured many
experimenters who tried to isolate it. In 1886, French chemistHenri Moissan succeeded. His
method of electrolysis remains the industrial production method for fluorine gas. The largest use
of elemental fluorine, uranium enrichment, began during the Manhattan Project.
Global fluorochemical sales are over US$15 billion per year. Because of the difficulty in making
elemental fluorine, ninety-nine percent of commercially used fluorine is never converted to the
free element. About half of all mined fluorite is used directly in steel-making. The other half is
converted to hydrofluoric acid, a precursor to other chemicals. The most important synthetic
inorganic fluoride is cryolite, a commodity that is critical for aluminium refining. Organic
fluorides have very high chemical and thermal stability. The largest market segment is
in refrigerant gases; even though traditional CFCs are now mostly banned, the replacement
molecules still contain fluorine. The predominant fluoropolymer is Teflon, which is used in
electrical insulation and cookware.
While a few plants and bacteria synthesize organofluorine poisons, fluorine has no metabolic
role in mammals. The fluoride ion, when directly applied to teeth, reduces decay. For this reason,
it is used in toothpaste and water fluoridation. A growing fraction of modern pharmaceuticals
contain fluorine; Lipitorand Prozac are prominent examples.
Early discoveries
Steelmaking illustration, Agricola text
The word "fluorine" derives from the Latin stem of the main source mineral, fluorite. The stone
was described in 1529 by Georgius Agricola, who related its use as a flux—an additive that helps
lower the melt temperature during smelting. Agricola, the "father of minerology", invented
several hundred new terms in his Latin works describing 16th century industry. For fluorite rocks
(schöne Flüsse in the German of the time), he created the Latin noun fluorés, from fluo (flow).
The name for the mineral later evolved to fluorspar (still commonly used) and then to fluorite.
Hydrofluoric acid was known as a glass-etching agent from the 1720s, perhaps as early as
1670.Andreas Sigismund Marggraf made the first scientific report on its preparation in 1764
when he heated fluorite with sulfuric acid; the resulting solution corroded its glass
container. Swedish chemist Carl Wilhelm Scheele repeated this reaction in 1771, recognizing the
product as an acid, which he called "fluss-spats-syran" (fluor-spar-acid).
In 1810, French physicist André-Marie Ampère suggested that the acid was a compound of
hydrogen with an unknown element, analogous to chlorine.Fluorite was then shown to be mostly
composed of calcium fluoride. Sir Humphry Davy originally suggested the name fluorine, taking
the root from the name of "fluoric acid" and the -ine suffix, similarly to other halogens. This
name, with modifications, came to most European languages, although Greek, Russian, and
some others (following Ampère's suggestion) use the name ftor or derivatives, from the Greek
υθόριος (phthorios), meaning "destructive".The New Latin name (fluorum) gave the element its
current symbol, F, although the symbol Fl was used in early papers
Later developments
During the 1930s and 1940s, the DuPont company commercialized organofluorine compounds at
large scales. Following trials of chlorofluorcarbons as refrigerants by General Motors, DuPont
developed large-scale production of Freon-12 in 1930. It proved to be a marketplace hit, rapidly
replacing earlier, more toxic, refrigerants and growing the overall market for kitchen
refrigerators. In 1938, Teflon was discovered by accident by a recently hired DuPont Ph.D., Roy
J. Plunkett. While working with a cylinder of tetrafluoroethylene, he was unable to release the
gas although the weight had not changed. Scraping down the container, he found white flakes of
a polymer new to the world. Tests showed the substance was more resistant to corrosion and had
better high temperature stability than any other plastic. By 1941, a crash program was making
significant quantities of Teflon.
Large-scale productions of elemental fluorine began during World War II. Germany used high-
temperature electrolysis to produce tons of chlorine trifluoride, a compound planned to be used
as an incendiary. The Manhattan project in the United States produced even more fluorine.
Gaseousuranium hexafluoride was used to separate uranium-235, an important nuclear explosive,
from the heavier uranium-238. Because uranium hexafluoride releases small quantities of
corrosive fluorine, the separation plants were built with special materials. All pipes were coated
with nickel; joints and flexible parts were fabricated from Teflon.
In the 1970s, concern developed that chlorofluorocarbons were damaging the ozone layer. By
1996, almost all nations had banned CFCs, and commercial production ceased. Fluorine
continued to play a role in refrigeration though: hydrochlorofluorocarbons (HCFCs)
and hydrofluorocarbons (HFCs) were the replacement refrigerants
Fluorocarbons
Organofluoride production consumes over 40% of hydrofluoric acid (over 20% of all mined
fluorite). Within organofluorides, refrigerant gases are still the dominant segment, about 80% on
a fluorine basis. Fluoropolymers are less than one quarter the size of refrigerant gases in terms of
fluorine usage but are growing faster. Fluorosurfactants (materials like Scotchgard, used
in durable water repellents) are a small segment in mass but are over $1 billion yearly revenue.
Refrigerant gases
Traditionally chlorofluorocarbons (CFCs) were the predominant class of fluorinated organic
chemical. CFCs are identified by a system of numbering (the R-number system) that explains the
amount of fluorine, chlorine, carbon and hydrogen in the molecules. The DuPont brand Freon
has been colloquially used for CFCs and similar halogenated molecules; brand-neutral
terminology uses "R" ("refrigerant") as the prefix. Prominent CFCs included R-11
(trichlorofluoromethane), R-12 (dichlorodifluoromethane), and R-114 (1,2-
dichlorotetrafluoroethane).
Production of CFCs grew strongly through the 1980s, primarily for refrigeration and air
conditioning but also for propellants and solvents. Since the end use of these materials is now
banned in most countries, this industry has shrunk dramatically. By the early 21st century,
production of CFCs was less than 10% of the mid-1980s peak.
Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) now serve as replacements
for CFC refrigerants; few were commercially manufactured before 1990. Currently more than
90% of fluorine used for organics goes into these two classes, in about equal amounts. Prominent
HCFCs include R-22 (chlorodifluoromethane) and R-141b (1,1-dichloro-1-fluoroethane). The
main HFC is R-134a (1,1,1,2-tetrafluoroethane)
Properties of Flourine
Atomic number 9
Atomic mass 18.998403
g.mol-1
Electronegativity according to Pauling 4
Density
1.8*10-
3 g.cm-3 at
20°C
Melting point -219.6 °C
Boiling point -188 °C
Vanderwaals radius 0.135 nm
Ionic radius 0.136 nm (-1)
; 0.007 (+7)
Isotopes 2
Electronic shell [ He ] 2s22p5
Energy of first ionisation 1680.6 kJ.mol -1
Energy of second ionisation 3134 kJ.mol -1
Energy of third ionisation 6050 kJ mol-1
Standard potential - 2.87 V
Discovered by Moissan in
1886