Structure of Atom (Part 3)

Discovery of Proton:

In 1886 Goldstein observed that in addition to cathode rays, other rays were also present in the discharge tube. These rays were traveling in opposite direction to cathode rays. He used a discharge tube having perforated cathode. He found that these rays passed through holes present in the cathode and produced a glow on the walls of the discharge tube. He called these rays as "canal rays".

The properties of these rays were as following:

i. These rays travel in straight lines in a direction opposite to the cathode rays.

ii. Their deflection in electric and magnetic field proved that these are positively charged.

iii. The nature of canal rays depends upon the nature of gas, present in the discharge tube.

iv. These rays do not originate from the anode. In fact these rays are produced when the cathode rays or electrons collide with the residual gas molecules present in the discharge tube and ionize them as follows:

v. Mass of these particles was found equal to that of a proton or simple multiple of it. The mass of a proton is 1840 times more than that of an electron.Thus, these rays are made up of positively charged particles. The mass and charge of these particles depend upon the nature of the gas in the discharge tube. Hence,different gases produce different types of positive rays having particles of different masses and different charges. Keep in mind that positive particles produced by a gas will be of the same type i.e. positive rays produced by the lightest gas hydrogen contain protons.

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