Химия. Экология. Медицина



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FRIEDRICH WÖHLER

Mohammad Shuaibat, group 25. Science adviser is Olga Levashova.


Friedrich Wöhler, was a German chemist, best known for his synthesis ofurea, but also the first to isolate several chemical elements.was also known for being a co-discoverer of beryllium, silicon andsilicon nitride, as well as the synthesis of calcium carbide, among others. In 1834, Wöhler and Justus Liebig published an investigation of the oil of bitter almonds. They proved by their experiments that a group of carbon,hydrogen, and oxygen atoms can behave like an element, take the place of an element, and can be exchanged for elements in chemical compounds. Thus the foundation was laid of the doctrine of compound radicals, a doctrine which had a profound influence on the development of chemistry.

Since the discovery ofpotassium by Humphry Davy, it had been assumed that alumina, the basis of clay, contained a metal in combination with oxygen. Davy, Oerstedt and Berzelius attempted the extraction of this metal, but failed. Wöhler then worked on the same subject, and discovered the metal aluminiumin 1827. To him also is due the isolation of the elements yttrium,beryllium, and titanium, the observation that "silicium" (silicon) can be obtained in crystals, and that some meteoric stones contain organic matter. He analyzed a number ofmeteorites, and for many years wrote the digest on the literature of meteorites in the Jahresberichteüber die Fortschritte der Chemie; he possessed the best private collection of meteoric stones and irons existing. Wöhler and Sainte Claire Deville discovered the crystalline form of boron, and Wöhler and Heinrich Buff discovered silane in 1857. Wöhler also prepared urea, a constituent of urine, from ammonium cyanate in the laboratory without the help of a living cell.



ROBERT BOYLE

Ahmad Murad Abughedah, group 25. Science adviser is Olga Levashova.


Louis Pasteur, a French chemist and microbiologist who is well known for his discoveries of the principles of vaccination, microbial fermentation and pasteurization. He is remembered for his remarkable breakthroughs in the causes and preventions of diseases, and his discoveries have saved countless lives ever since. Pasteur reduced mortality frompuerperal fever, and created the first vaccines for rabies and anthrax. His medical discoveries provided direct support for the germ theory of diseaseand its application in clinical medicine. Pasteur is best known to the general public for his invention of the technique of treating milk and wine to stop bacterial contamination, a process now called pasteurization. He is regarded as one of the three main founders of bacteriology, together withFerdinand Cohn and Robert Koch, and is popularly known as the "father of microbiology".

Pasteur also made significant discoveries in chemistry, most notably on the molecular basis for the asymmetry of certain crystals and racemization. He was the Director of the Pasteur Institute, established in 1887, till his death, and his body lies beneath the institute in a vault covered in depictions of his accomplishments in Byzantine mosaics.



SODIUM

Rami Mohammad Ali, group 25. Science adviser is Olga Levashova.


Sodium is a chemical element with the symbol Na (from Latin: natrium) and atomic number 11. It is a soft, silver-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23 Na. The free metal does not occur in nature, but instead must be prepared from its compounds; it was first isolated by Humphry Davy in 1807 by the electrolysis of sodium hydroxide. Sodium is the sixth most abundant element in the Earth's crust, and exists in numerous minerals such as feldspars, sodalite and rock salt. Many salts of sodium are highly water-soluble, and their sodium has been leached by the action of water so that chloride and sodium (NaCl) are the most common dissolved elements by weight in the Earth's bodies of oceanic water.

Many sodium compounds are useful, such as sodium hydroxide (lye) for soap-making, and sodium chloride for use as a deicing agent and a nutrient (edible salt). Sodium is an essential element for all animals and some plants. In animals, sodium ions are used against potassium ions to build up charges on cell membranes, allowing transmission of nerve impulses when the charge is dissipated. The consequent need of animals for sodium causes it to be classified as a dietary inorganic macro-mineral.

Sodium at standard temperature and pressure is a soft metal that can be readily cut with a knife and is a good conductor of electricity. Freshly exposed, sodium has a bright, silvery luster that rapidly tarnishes, forming a white coating of sodium hydroxide and sodium carbonate. These properties change at elevated pressures: at 1.5 Mbar, the color[clarification needed] changes to black, then to red transparent at 1.9 Mbar, and finally clear transparent at 3 Mbar. All of these allotropes are insulators and electrides.

When sodium or its compounds are introduced into a flame, they turn it yellow, because the excited 3s electrons of sodium emit a photon when they fall from 3p to 3s; the wavelength of this photon corresponds to the D line at 589.3 nm. Spin-orbit interactions involving the electron in the 3p orbital split the D line into two; hyperfine structures involving both orbitals cause many more lines.

Sodium is generally less reactive than potassium and more reactive than lithium. Like all the alkali metals, it reacts exothermically with water, to the point that sufficiently large pieces melt to a sphere and may explode; this reaction produces caustic sodium hydroxide and flammable hydrogen gas. When burned in dry air, it mainly forms sodium peroxide as well as some sodium oxide. In moist air, sodium hydroxide results. Sodium metal is highly reducing, with the reduction of sodium ions requiring −2.71 volts. Hence, the extraction of sodium metal from its compounds (such as with sodium chloride) uses a significant amount of energy. However, potassium and lithium have even more negative potentials.

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