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                                         RARE OCCURRENCE AND GAS DISCOVERY
          While the main element in the group of halogens (Cl, I, Br and F) have been discovered in time 120 years, the main elements of group rare gases (He, Ar, Ne, Kr, Xe) were found in only 30 years and making abstraction of helium found in the Sun was about spectral, other 4 elements were isolated in only four years (1894-1898). The first of the latter, argon was discovered by Sir JWS Rayleight and Sir W.Ramsay and then the other 3 by Sir W.Ramsay and Sir MWTravers. After the properties were known, then curious, not combine with any other element, the English nobles seem normal to be called "noble gases,. Later due to the same properties were called "inert gases, or, as the place occupied in periodic table elements" zerovalente, and then because of the rarity with which are found in the atmosphere, "rare gases,. N effort discovery of rare gases, a special weight that must be taken into account was the fact that none of these gases had no chemical eractivitate to other elements, therefore the name of elements "zerovalente,. Stopping the achieve any chemical combinations with these gases, their isolation could done only by physical means: identification with the help spectroscopy, and the separation by distillation fractionated of various fractions derived from liquid air. Chemical methods were used only to eliminate the other components of air: oxygen, nitrogen, carbon dioxide, water vapor, etc..  In recent years, efforts made by oamanii researchers found that some rare gases, especially xenon, in the presence of highly reactive elements such as oxygen and fluorine, under the influence of great energy, can give some combinations of exceedingly Otherwise labile, such as xenon difluoride (XeF2), tetrafluorura xenon (XeF4) and carbon dioxide, xenon (Xe O2), the latter being highly explosive. In 1962, N.Bartlett, treating xenon hexafluoride get hexafluoroplatinatul xenon platinum. Obviously, these combinations have, at least for now scientific interest. But history is fascinating discoveries rare gas them, for blends, however it seems curious passion for science with progress of researchers productiei.Francezul G. Claude (1870-1960) performs a method for ammonia synthesis and expansion in discovering and liquefying method gas intake method brings serious and rare gas discovery efforts aer.Astfel G. Claude Ramsey gives the residue obtained after distilled over 100t of liquid air. ITR was indeed a tremendous amount for the researcher who sometimes barely able to collect minor amounts of gas discovered, you can submit them spectrale.Ramsay analysis, this time with Prof. Morre in Indianapolis, they start to analyze this particular residue pretios.La began removing the remaining oxygen with phosphorus, nitrogen and magnesium heated to red, hydrocarbons and carbon monoxide and hydrogen with lime and water vapor with phosphoric anhydride. Almost exclusively gases remain so rare. By fractionation of the mixture obtained all inert gases in sufficient quantities to be able to study their properties.
Enthusiasm provoked discovery time or rare gases can be easily understood from the writings of Ch Moureu in 1911: "Their complete inertia puts them to say so on the edge of chemistry. She em ensure inalterabilitate eternal, what them protects against all cataclysms asronomiei and geology on which them crosses, remaining always completely healthy and nevatamate.Gratie between others their condition gaseous their access easy in all fluids and in all atmospheres where those five family members traveling freely and without ever separating,.


             Towards the end of 1890, scientists knowledge about the chemical composition of the atmosphere were more advanced than a century before, so most of the years 1780.Intr fact, in the second half of the eighteenth century, a number of extremely important discoveries made only a few years have made it possible knowledge of the main components of the atmosphere.
After the year 1755, J. Blake (1728-1799) had done experiments and show the role of carbon dioxide in 1766 H.Cavendish discovered hydrogen, nitrogen D. Rutherford (1774), J. Priestley discovered his research will oxigenul.Din 1777 Lovoisier the firing and the role of oxygen in combustion and respiration, and in 1783 Cavendisch show that air contains (by volume) 20.83% oxygen and 79.11% nitrogen.
In 1785, all H. Cavendish, among his many experiences, is one that would become of great importance, but only over a century. English chemist had a fixed amount of air and after removing CO2 and adds oxygen, electrical sparks go and get some brown fumes, nitrogen oxides, which dissolve in water showed the presence of nitric acid. So managed to combine the action of nitrogen and oxygen discharges electrictrice. Removing the excess oxygen tarry in glass bowl gas amount. Repeating several times this experience, finds that the device remains 1/120 part of the volume of air taken initially experienced and bonded unchanged. Unbundled after 75 days for gaseous mixture was subjected to electrical discharges. However, Cavendish found that "nitrogen omogen.Aceasta regarded as a body experience, although published fell into oblivion for more than a century secol.Catre end becomes the object of controversy a hypothesis that a doctor had made W.Prout English ( 1786-1850) since 1815, who claimed that all chemical elements are formats at the base of hydrogen, which would be the element primordial (protylul of Aristotle). A first consequence of this hypothesis, if confirmed would lead to the conclusion that all atomic weights must be intergi numbers (multiples of hydrogen) when in reality there were many fractional (chlorine 35.5 27.4-beryllium-aluminum 9.4 etc ).
Some chemists, led by L.Gmelin (1788-1853), accept from the beginning Prout's hypothesis, in contrast others, led by J.Berzelius and J.Stas (1813-1891) whose extreme precision experiments to determine authority did the atomic equivalents were definitely born polemic defense against ei.Din a clear need to be recalculated weights atomice.John William Stuart (1842-1919), which since 1873 is known as Lord Rayleigh, an eminent physicist Cavendish Laboratory, University of Cambridge and who later was to be the director of this laboratory, was also interested in clarifying Prout's hypothesis. Thus, in 1882 he started research on water composition and thus the Rayleigh oxigen.Fizicianul components hydrogen and wanted to get involved in solving this problem but it is clear that this problem can not be solved only by him. I needed a chemist to get involved in solving this problem and solve commit ei.Dintre chemists who show particular interest was Scot Williams Ramsey (1852-1916) ten years younger than Rayleigh. Ramsey DEPA what in childhood had been passionate of music and football, starts his Student at University di Glasgow-his hometown-in year 1869, year in which Mendeleev presented famous or system of the elements of which have to use with great success later even Ramsey.
Ramsay after studying Rayleigh's article, is convinced that the difference between air and nitrogen densities derived from combinations of chemicals in the air is proof that there is still an unknown gas heavier than nitrogen. It chooses a chemical method for finding gas that in his experience Cavendish remained bonded to nitrogen even after lightning. Through a very severe air purification (removing CO2 and water vapor). Oxygen is then fixed copper remained hot and nitrogen is passed over heated magnesium and magnesium nitrates Note that (N2Mg3). The oxygen will fixed very easily on copper warmed, and nitrogen is passed over magnesium, for 10 days.

As the gas volume is smaller, its density increased. After 10 days Ramsey managed to get this new gas cubic 100cm determining its density which finds 19,086.
   After celebrating a year of collaboration between Ramsay and Rayleigh takes place the Natural Sciences British Society Congress, on 13/08/1984 at Oxford. On this occasion the two shows new element called "On a new gas atmosphere,. But the new element not yet have a name and is called ARGON HGMadan president's suggestion that the Greek language is still lenes.Argonul is studied and the kinetic theory of gases. Ramsey finds that gas found is monoatomic and therefore could not be a body compus.Aceasta discovery of a gas in air has a resounding successful in scientific circles of the epoch. But far from being finished an activity, success was likely to stimulate further research that would bring the discovery of a family of rare gases.
Discovery News finds argon H. Helmholz (1821-1894), one of fondatoriin principle of energy conservation, paralyzed on his deathbed and say that after I read it is new, maribundul would have said: "I always thought there is something extra in the atmosphere,

           For 18 august 1868 announced a solar eclipse, which would be entirely in India. One of the most passionate astronomers from this event was the Frenchman Pierre ICJanssen (1824-1907), who, after making astronomical observations and spectral mentioning returning to France he found a bright yellow line D3, which coincides with sodium and may not be reproduced in the laboratory or with other substances. Janssen not wanted to go further, but JNLocker (1836-1920), astronomer English and Director Observatory solar physics noticed and he in 20oct 1863, line yellow's Janssen and has published this finding in 1869.
Interpreting observations and results of Janssen, Lockyer found that yellow line that appears in the spectrum protruding show that it is a new element which they called helium. So they said, "Behold an element that is not found on Earth, but is present in the Sun,. Obviously things were not too convincing and some have criticized this statement. Is the temperature conditions of the Sun, hydrogen could not give the yellow line? Things will clarify only when helium will be found on Earth. Been 10 years old when in 1881, L. Palmieri found in the spectrum of the gaseous products of Vesuvius yellow line of helium. So, this new gas exist on Earth. He is identified spectral moment, but spectroscope and its accuracy has been proved that all researchers were able to correctly interpret the results. The fact that helium is found on Earth led researchers to look for it with more hope.
In 1895, Ramsay is informed by mineralogist Mayers on experiences made by the chemist W. Hillerand the U.S. Geological Bureau. Hillebrrand attacking uranium ore with hot concentrated sulfuric acid, finds that emit nitrogen gas with similar properties. He did research spectrum, and in "Note, which published it wrote that" could be a new gas if his colleagues not kidding,,.
Ramsey system or M. Matthews, buy cleveita (a uranium mineral) and treating it with hot sulfuric acid gas release notes mentioned by Hillebrand.
After you manage to isolate a few cubic centimeters, composed Ramsay's yellow line spectrum finds that Janssen discovered the sun and upon which Lockyer had appointed new helium gas.
If the discovery of argon, Ramsay worked with Rayleigh two years, identifying helium did it in two days. Shortly after Hamilton P. Cade (1874-1943), reveals the presence of helium in natural gas in Kansas.

Krypton and neon
          So in 1895 were known two inert gases. Ramsay concluded that after four atomic weight helium and argon with atomic greuattea (40 should be another whom he described elements and properties and atomic weight 20.0945. According argon we should also exist two other atomic weights of 82 and 129.
During this time he found an associate chemist Morris William Travers youngster (1872-1961) who at 21 just finished her doctorate and comes as assistant to Ramsey. These two turn their research into mineral, mineral and meteorites, but not getting any results. In 1898 are turning back to the atmosphere, although the percentage of nitrogen, oxygen, argon and CO2 was almost 100%.
During this time great progress had been made in the liquefaction of air: French LP Calletet (1832-1913), Swiss R. Pictet (1842-1929) and C. Linde (1842-1934) in Germany and W. Hampson (1854 - 1926) in M. Kingdom made cars and perfected for this purpose.
Hampson's Ramsay sends one of the first air esantoane liquid cubic 100centimetri. Ramsay and Travers removed by fractional distillation almost the entire nitrogen and oxygen, and the few cubic centimeters left them subject to spectral analysis in identifying argon. But still appear new spectrum consisting of two lines, one yellow and one green. With the experience they had, and realized that there may be a gas discovered so far, but a new element which they called the same evening KRIPTON (in Greek "hidden,,). It was in May 30, 1898, after four years of research.
Shortly before the completion happy, Ramsay, whose spectroscope did not seem to be of great sensitivity, sent a sample of Crookes (which all spectral discovered thallium in 1861) confirm its existence krypton and Crookes says, "krypton is helium,. Ramsay had yet to Krypton.
Determining the density and atomic weight of krypton then found to be (85. During periodic table had placed between bromine and rubidium. But the element of He and Ar have not been revealed, he had sought a more volatile fraction of residue liquid air .
Thus, Ramsay and Travers introduce liquid argon in the air after it liquefies, and it solidifies and then distills it with very great caution under reduced pressure. Collecting first portion resulting from evaporation argon, get a piece that analyzed the spectroscope, gives a new spectrum with a red line. They call the new neon gas (after the Greek word "new,,). It was in June 1898. Density of atomic mass 10 and 20, neon is just the item to be placed between He and Ar.


         Ramsay and Travers continued research, chemist Ludwig Mond using (1839-1900), which provides a liquid car air, with which fail to reach temperatures of 253 degrees C. Thus they are able to liquefy large amounts air. They liquefy argon, it fractional methodically and after eliminating KRIPTON always remains few small bubbles in coloring blue, which presented a characteristic spectrum: XENON (after cuv. Greek "stranger,,). It was July 12, 1898.
Thus Ramsey and Travers discovered the 5th inert gas, processing 77.5 million liters of free air, getting only 300 cubic centimeters of xenon.
All these elements constitute a family of elements characterized by: monatomic molecules, zerovalente and placed in periodic table between alkali metals and halogens

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Simbol chimic : N
Masa atomica : 14
Numar de masa “Z”: 7
Azotul se gaseste in grupa a V-a principala ai in prima perioada in sistemul periodic.
Azotul este un caz incolor, inodor, insipid si non-toxic. El poate fi condensat intr-un lichid incolor si apoi compresat intr-un solid incolor si cristalin.
Nitrogenul are denistatea cu putin mai mica decat a aerului si este mai putin solubil in apa decat oxigenul. El nu intretine viata fiintelor care il respira.
Temperatura de topire a azotului este de – 210, 01 °C , in timp ce cea de fierbere este de – 195, 79 °C.
STARE NATURALA: Azotul este unul dintre gazele extrem de raspandite in natura. El se gaseste atat in stare libera cat si sub forma de compusi:
In stare libera, azotul reprezinta 78% din volumul aerului atmosferic.
Compusii azotului sunt:
-anorganici ( amoniac, azotati, etc. )
-organici (uree, proteine )
Azotul de gaseste intr-o proportie de la 1 la 10 % in fiecare din organismele vii.


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