Atomic Theory
In ancient Greek the word atom meant the smallest indivisible particle that could be conceived. The atom was thought of as indestructible; in fact, the Greek word for atom means "not divisible." Knowledge about the size and make up of the atom grew very slowly as scientific theory progressed. What we know/theorize about the atom now began with a core theory devised by Democrotus, a Greek philosopher who proposed that matter consisted of various types of tiny discrete particles and that the properties of matter were determined by the properties of these particles. This core theory was then modified and altered over years by Dalton, Thompson, Rutherford, Bhor, and Chadwick. The atoms original structure was simple, but as more and more research was done the atom became more complex and puzzling The five atomic theories of the past two centuries represent the sudden advancement of science in modern times. Beginning with a basic theory on the behavior of atoms to the current model, some changes have been made, and some ideas are still the same. Ancient Greek philosophers believed that everything was made up of invisible particles called atoms. Since then the theory of atoms did not progress until 18
The first of these modifications came in 1897 when J.J. Thomson discovered the electron. Based on the work of William Crookes and his "Crookes tube" (Cathode-ray tube), Thomson discovered a negative charged particle was the cause of the light produced by the cathode-ray tube. He also discovered that these particles are present in all elements. These cathode-ray particles are now known as electrons. Soon after the discovery of electrons the proton was discovered. This led Thomson to conclude that there were an equal number of both particles present in the atom. 2. All atoms of the same element are exactly alike; in particular, they John Dalton was the first scientist to compose a theory of matter based on atoms. Dalton's atomic theory is based on four concepts. He stated: Using Rutherford's model of the atom as a miniature solar system, Bohr developed a theory by which he could predict the same wavelengths scientists had measured radiating from atoms with a single electron. However, when conceiving this theory, Bohr was forced to make some startling conclusions. He concluded that because atoms emit light only at discrete wavelengths, electrons could only orbit at certain designated radii, and light could be emitted only when an electron jumped from one of these designated orbits to another. Both of these conclusions were in disagreement with classical physics, which imposed no strict rules on the size of orbits. To make his theory work, Bohr had to propose special rules that violated the rules of classical physics. He concluded that, on the atomic scale, certain preferred states of motion were especially stable. In these states of motion an orbiting electron (contrary to the laws of electromagnetism) would not radiate energy. The completed model that they came up with is the model that students now learn about in school. These scientists did exactly what scientists are supposed to do: test, experiment, and an
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Approximate Word count = 1308
Approximate Pages = 5 (250 words per page double spaced)
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