The Evolution Of The Atomic Theory :: essays research papers

The Evolution of the Atomic scheme     The five atomic possibilitys of the past two centuries represent the sudden forwarding of science in modern times. Begining with a basic surmisal on thebehavior of atoms to the current model, some changes receive been made, andsome ideas are remedy the aforementioned(prenominal). 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 scientist to compose a theory of matter basedon atoms. Daltons atomic theory is based on four concepts. He stated     "1. All elements are 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 havedif ferent masses.     4. Compounds are formed by the joining of atoms of two or moreelements." 1     All of Daltons ideas account for the laws of definate and multipleproportions and the law of preservation of mass. Some of Daltons points arestill thought to be true, but everyplace 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 controvert charged particle was thecause of the light produced by the cathode-ray tube. He in any case discovered thatthese particles are present in all elements. These cathode-ray particles are outright known as electrons. Soon after the discovery of electrons the protonwas discovered. This led Thomson to give over that ther were an equalnumber of both particles present in the atom.     Twelve years la ter Lord Ernest Rutherford was experimenting with of import particles. He shot a germinate of them at a peice of gold foil surroundedby zinc-sulfide. When an alpha particle strikes ZnS it produces a flash oflight. The particles mostly stayed in a unvaried stream through the foil, but afew were deflected. This led Rutherford to belive that on that point must be a small,dense cluster of protons in the center of the atoms to deflect the smallnumber of particles.      Neils Bohr was the next physicist to advance the atomic theory. Heexplained what Rutherford could not about how the electron could stay inorbit more or less the nucleus. When the electron has little energy it is closer to thenucleus, when it absorbs more energy it travels farther from the nucleus. There is a definate number of electrons that can be in the same orbit. Whenthe orbits closest to the nucleus are filled the atom is at a ground state.