The Oddessey of the Atom: From Democritus to The Periodic Table. Part 1

The Early Days

The idea of atom was first disussed in detail by Democritus in Greece and Kashyapa in India. The central idea of the theroy they proposed was that there will be a limit which you cannot cross, when cutting matter in half and then in half again and so on. Like you cannot break a brick into two (you’re strong if you can do that) after you have broken it into crumbles, you can break the matter into two after that limit. The particle at the limit was called “atomio” by Democritus and “Parmanu” by Kashyapa.

The Cathode Ray Experiment and the discorvery of Electrons

Skip for ward again by a hundered years or so. Maxwell had just published a new theory on electromagnetism. Scientists all over the world were trying to use it to explain many properties of matter. One such scientist was JJ Thomson. In 1898, Thomson was using a vaccum tube to hold a couple of carbon electrodes connected to a circuit and filling it with different gasses in hopes of finding a new element. He accidentally left a phosphorus sheet in the tube when changing the electrodes. Then as he fired up the circuit, he saw that the phosphorus screen lit up. According to Maxwell’s theory, the rays must have went from the Cathode to the Anode. He once again used different gasses and all of them showed the same result. This meant that there was a negatively charged particles that were travelling. He visualised these to be rays and named this stream of particles “Anode Rays” and the particle “electron”.

Discovery of the Proton

By modifiying the apparatus so that the screen was behind the anode, scientists were able to discover “Anode Rays” and the bundles of these rays were named “Protons”.

Discovery of the Nuetron

Neutrons were discovered in 1919 by James Chadwick. It is kind of hard to explain the experiment he used, because it uses teh principles of photoelectric effect, but he bombarded a thin sheet of Berillyum with α particles (alpha particles, which are Helium atoms without any electrons) and it produced a light. This was in accordence of photoelectric effect and hence an electrically neutral particle was discovered. This was named “Neutron”.



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