The Atomic Theory

1649 WordsMar 29, 20177 Pages
The history of the atomic theory is thoroughly extensive. It had all started around 400 BCE when few people believed in an atomic theory, that atoms are building blocks. Democratic believed matter was made up of tiny particles. He called them atomos. Democratic is Leucippus’ most infamous pupil Later in history, the law of definite proportions was discovered. Two samples of given compounds are made of the same elements in exactly same proportions by mass regardless of the size or sources of the samples. After this came the law of conservation of mass and law of multiple proportions. Around 1808, John Dalton came up with a different atomic theory. He used Greek concept of the atom and all of the laws previously mentioned to acquire his…show more content…
Electrons were first discovered not by examining the atomic theory, but studying electricity. English physicist J.J. Thomson contributed to this. He first pumped most of the air out of a glass tube. Next, he applied voltage to electrodes, which were on both ends of the tube. Thomson had observed a beam that came out of the cathode and struck the sides of the glass. He decided to call these beams, cathode rays. This tube that Thomson had, is actually used today in television, radar displays, and more. After finding the rays, Thomson found that electrons have a negative charge. Because the cathode ray came from the negatively charged cathode, he believed it must be negatively charged. By proving this, Thomson tested how electric and magnetic fields affect the cathode rays in the discharge tube. He also had another experiment, using a small paddle wheel in the path of the rays. Both of these experiments proved the existence of the particles, electrons who are members of the family of leptons. To go further into this, Thomson believed that electrons were embedded in a positively charged ball. He made an actual model of this, which is known as the plum-pudding model. To go even further, scientist Robert A. Millikan did an oil droplet experiment to determine the electric charge of these electrons. However, in 1909, Ernest

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