Element

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 4s1

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 zinccarbon 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 corrosionresistantaluminium 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 4s2

Energy of first ionization

716 kJ.mol -1

Energy of second ionization

1489 kJ.mol -1

Standard potential Discovered

- 1.05 V ( Mn2+/ Mn ) 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 technetium97 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 ruthenium99.

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 selfcontained 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 Electronic shell Discovered by

9 [ Kr ] 4d6 5s1 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 alphacapture 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 redorange 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 lithiumbased 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 leadacid or 1.5 volts for zinc-carbon cells. Because of its low atomic mass, it also has a high chargeand 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

1s22s1 or [He] 2s1

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 Discovered by

+ 0.854 V ( Hg2+/ Hg ) 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 sixthhighest 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 molybdenumdoped 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 5s1

Energy of first ionization

651 kJ.mol -1

Standard potential Discovered by

- 0.2 V 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

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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. 

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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 Electronic shell Energy of first ionization Energy of second ionization Energy of third ionization

7 [ Xe ] 5d1 6s2 539 kJ.mol -1 1098 kJ.mol -1 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 Ionic radius Isotopes

0.162 nm 0.112 nm (+2) ; 0.070 nm (+4) 20

Electronic shell

[ Kr ] 4d10 5s25p2

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 Discovered by

3929.3 kJ.mol -1 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 protactinium234. A more stable isotope (231Pa) 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 234Pa 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, 231Pa 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 232Th + n → 231Th + 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 231Pa 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 Atomic mass

91 231.0359 g.mol -1

Electronegativity according to Pauling Density Melting point Boiling point

1.5

15.37 g.cm-3 at 20°C 1600 °C unknown

Vanderwaals radius

unknown

Ionic radius

unknown

Isotopes Electronic shell Discovered by

5 [ Rn ] 5f2 6d1 7s2 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 hightemperature 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 (1,2dichlorotetrafluoroethane). 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 Atomic mass Electronegativity according to Pauling Density Melting point Boiling point Vanderwaals radius Ionic radius Isotopes Electronic shell Energy of first ionisation Energy of second ionisation Energy of third ionisation Standard potential Discovered by

9 18.998403 g.mol-1 4 1.8*103 g.cm-3 at 20°C -219.6 °C -188 °C 0.135 nm 0.136 nm (-1) ; 0.007 (+7) 2 [ He ] 2s22p5 1680.6 kJ.mol -1 3134 kJ.mol -1 6050 kJ mol-1 - 2.87 V Moissan in

1886