ATOMIC THEORY DEVELOPMENT & HIGH COORDINATION COMPOUNDS ( CH 2)

From the times of the ancient Greeks to the present, the model and the atomic theory continues to evolve. Through the model and theory of the atom, we can determine the structure of an atom. The development can not be separated from the efforts of scientists such as Democritus, John Dalton, JJ Thomson, Rutherford, Chadwick, ownership, Niels Bohr, Schrodinger, de Broglie and Heisenberg.
1. Atomic Theory Democritus (460 BC-370 BC)Democritus developed a theory of constituent materials. According to Democritus if a matter of a continuous cut would be obtained when the fundamental particles called atoms (Greek: atomos = not divided). This argument was rejected by Aristotle (384-322 BC), who argued that matter is continuous (material can be cut continuously until infinite). Aristotle's theory in favor Empedocles, that matter is made up of fire, water, earth and air. Around the year 1592 - 1655 Gasendi suggested that atom is the smallest part of a substance.2. Dalton Atomic Theory (1803)John Dalton reveals that:a. Atom is the smallest part of a substance.b. Simple spherical atoms are very small, can not be divided, created or destroyed.c. Same element contains the same atoms.d. Atoms have the same kind in every way, while the different atoms have different properties.e. Chemical reactions occur due to the merging and splitting of atoms.f. When atoms combine to form molecules. When atoms are joined together will form the molecular elements, whereas when atoms combine different molecular compounds are formed.Weakness of Dalton's atomic theoryIn the further development of the facts are found that can not be explained by this theory, among others:a. Unable to explain the electrical properties of the material.b. Unable to explain how atoms bond together.c. Dalton atomic model can not explain the difference between a single atom element with another element.These weaknesses can be explained after it was discovered some subatomic particles, such as electrons discovered by Joseph John Thomson in 1900, the discovery of proton particles by Goldstein in 1886.Excess Dalton's atomic theorya. Can explain the Law of Conservation of Mass (Lavoisier law)b. Still can explain Comparative Law (Law Proust)
3. Thomson Atomic TheoryBased on experiments on electrical conductivity through a vacuum tube / tube pengawan charge (discharge tube) or a cathode ray tube. In a cathode tube gas pressure inside the tube can be adjusted via the suction pump (vacuum pump). At sufficiently low pressure and high voltage (several thousand volts), the gas in the tube would glow with light colors depending on the type of gas in the tube (gas neon red, yellow sodium gas). If the gas pressure is reduced, then the area in front of the cathode will be dark. Dark areas will increase if the gas pressure in the tube continues to be reduced, eventually the entire tube to be dark, but the front of the cathode tube glow with a greenish tint.Through the experiments it can be shown that the perpendaran was caused by a radiation emanating from the surface of the cathode towards the anode. Because coming from the cathode, the radiation is called cathode rays. The results of the cathode tube experiment proves that there are negatively charged particles in an atom because the beam can be deflected toward the positive pole of the electric field. The next is a cathode ray particles and negatively charged particles, Thomson was named after the electron

 U.S. researchers have solved a note of the compound with the highest coordination number - number of the series of atoms that are able to bind. These compounds, thorium aminodiboranate, Th (H3BNMe2BH3) 4, has a core of 15 hydrogen atoms bind to separate thorium, breaking the previous calendar notes, which are held by other compounds, one by one.To obtain a high coordination number of an atom is surrounded by a great need of small atoms first, shown in a way that is not filled with atoms of one another. 'Both electronic factor and Steris - compaction - can limit the number of koordinasiannya, "said Gregory Girolami, from the University of Illinois at Urbana-Champaign, one of the team leaders. 'The thorium complex electronic factor and does not limit the amount of coordination is almost entirely dictated by compacting it.'High coordination number of a compound relies on thorium which becomes very large and the very small hydrogen atom. 'What we have done is to describe how to make a compound in which the thorium atoms form hydrogen bonds only with it, "said Girolami. There are only three other thorium compounds that can be set, but one of the coordination number is 12 and the rest of the other two remain unknown. "We also use a coordinating group which is compact and form a compound organic ligand, [so] binding on thorium atom with four hydrogen atoms on the purpose and features increased kestabilitasannya, 'explains Girolami.Thorium compounds representing 15 first coordinate complex (orange: Th, gray - brownish gray: B, purple: N, black: C, blue: H)While the new compounds have no immediate practical application, a high coordination number is very useful, says Girolami, in keeping the metal complex 'in isolation is good', which in turn will improve other properties such as vapor pressure, which is useful once in several applications such as disposition metal from the gas phase.Keith Izod, an expert on chemical coordination at Newcastle University in the UK, said, 'Although the determination of the amount of coordination can only be subjective, 15 coordinate thorium compounds were reported recently - this new press limit the maximum amount of coordination investigated so far.''This is a good structure which may be more than just suspicion than any chemical - although there is nothing wrong with that! Overall this is an interesting piece of work.