![]() ![]() At this stage the glass wall of the discharge tube opposite to the cathode, start glowing with a faint greenish light. Thomson observed that, when a high voltage (~ 10,000 volts) is applied between the electrodes fitted in discharge tube, through a gas at a very low pressure (~ 10 -3 Torr), some invisible radiations are emitted from the cathode. ![]() William Crookes discovered that the gases start conducting electricity under reduced pressure. The electron, proton and neutron are the main fundamental particles of an atom.ĭiscovery of electron – study of Cathode rays: The researches show that atom can be divided into about 200 sub atomic particles. Infact, the atom as the whole is electrically neutral as number of protons in it is equal to number of electrons. John Dalton (1808–1809) could give a scientific basis to the old ideas or hypothesis by proposing his famous atomic theory called as Dalton’s atomic theory, regarded the atom as the ultimate particle of matter and considered to be indivisible and indestructible. ![]() These earlier ideas were mere speculations and there was no way to test them experimentally. The word ‘atom’ has been derived from the Greek word ‘ a–tomio’ means ‘which cannot be cut’ or ‘non–divisible’. Later on Democritus, a Greek Philisopher also proposed that the matter is made up of extremely small particles, i.e., atoms are fundamental building blocks of the matter. Maharshi Kanad the Indian Philosopher proposed that matter is made up of small particles called Parmanu and anu. “The rich diversity of chemical behavior of different elements can be traced to the differences in the internal structure of atoms of these elements”. ![]()
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