History Of Atomic Theory

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The atomic theory has come a long way since 400 B.C.E when the atomic model looked like a billiard ball, it is a very fundamental part of modern chemistry. About twenty four hundred years ago the first supporters of an atomic theory were the Greek philosophers Leucippus and Democritus who proposed the theory that matter could not be divided into smaller and smaller pieces over and over, he called these tiny pieces atomos. This comes from the meaning “cannot be cut”. He thought that atoms were small, hard and were made up of the same things but came in all different shapes and sizes. Atoms were infinite, always jiggling and joining together. More than two thousand years later, in the early 1800’s the Chemist John Dalton came across a new theory …show more content…
This model shows that atoms are made from a positively charged substance with negatively charged electrons all throughout, representing raisins in plum pudding. Not long after the plum pudding model, Thomson started to study the passage of an electric current through a gas. This is where the cathode ray experiment comes into play and greatly contributed to the modern understanding of chemistry. If you have ever seen a neon sign, this is a modern example of a cathode ray. These signs used corpuscles, which are tiny particles regarded as constituent of light which makes the neon sign light up. His first experiment was a cathode ray experiment that took place inside of a discharge tube which was glass with a metal cylinder containing two slots on the end of the tube which lead to electrometers that could read and measure small electric charges. He sent a magnetic charge across the tube and there was no activity recorded by the electrometers. This means the charge had been sent away from the …show more content…
In his third and final experiment he later concluded that cathode rays were made up of particles that were from within the atoms. Thomson called these negatively charged particles we know today as electrons. After this experiment, led to the experiment and finding of the nucleus through the gold foil experiment. Ernest Rutherford, in 1909 , tried firing a stream of positively charged particles in a thin sheet of gold foil. Most of the positively charged particles known as protons passed through the gold atoms in the foil without changing their direction at all. Not all of the particles went through however. Some of these hit the gold sheet and bounced away just as if they hit something solid in the middle of the foil. Rutherford knew positive charges repel against other positive charges. In conclusion, he discovered that most of the space in the gold foil was open space and so this disproved the plum pudding model Rutherford has earlier created. Also in this experiment he concluded the atom had a dense positively charged center, he called this the

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