The Evolution Of The Atomic Theory :: essays research papers

The Evolution of the Atomic Theory     The five nuclear theorys of the past twain centuries re defend the suddenadvancement of science in modern times. Begining with a basic theory on thebehavior of atoms to the current model, some changes get been made, andsome ideas be still the same. Ancient Greek philosophers belived thateverything was made up of invisible particles called atmos. Since then thetheory of atoms did not progress untill 1803.     John Dalton was the first-year scientist to compose a theory of matter basedon atoms. Daltons atomic theory is based on four concepts. He stated     "1. totally elements be composed of atoms, which are indivisable andindestructable particles.     2. All atoms of the same element are exactly alike in particular, theyhave the same mass.     3. Atoms of different elements are different in particular, they havedifferent masses.      4. Compounds are formed by the joining of atoms of two or moreelements." 1     All of Daltons ideas sexual conquest for the laws of definate and multipleproportions and the law of conservation of mass. Some of Daltons points arestill archetype to be true, but over time this origional theory has been modifyed. The first of these modifications came in 1897 when J.J. Thomson discoveredthe electron. Based on the work of William Crookes and his "Crookes tube"(Cathode-ray tube), Thomson discovered a negative charged particle was thecause of the abstemious produced by the cathode-ray tube. He also discovered thatthese particles are present in all elements. These cathode-ray particles arenow known as electrons. Soon later the discovery of electrons the protonwas discovered. This led Thomson to conclude that ther were an equalnumber of both particles present in the atom.     Twelve years later Lord Ernest Rutherford was experimenting withalpha particles. He shot a stream of them at a peice of gold check surroundedby zinc-sulfide. When an alpha particle strikes ZnS it produces a flash oflight. The particles broadly collared in a constant stream through the foil, but afew were deflected. This led Rutherford to belive that there must be a small, sullen cluster of protons in the middle of the atoms to deflect the smallnumber of particles.      Neils Bohr was the adjoining physicist to advance the atomic theory. Heexplained what Rutherford could not about how the electron could stay inorbit around the nucleus. When the electron has little energy it is juxtaposed to thenucleus, when it absorbs more energy it travels farther from the nucleus. There is a definate number of electrons that good deal be in the same orbit. Whenthe orbits closest to the nucleus are fill up the atom is at a ground state.