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The Discovery of Protons


After it was found that all atoms contain one or more electrons, which are negatively charged, scientist naturally searched for a positively charged particle. Toward the end of the nineteenth century, a number of physicists studied positively charged rays in discharge tubes containing hydrogen.

In 1919, Ernest Rutherford, a student of J.J. Thomson announced his discovery of certain charged particles behind the cathode. These particles were called canal rays. On analysis, they were found to be:

- positively charged.

- heavy.

- of the same mass order as the atoms or molecules of the gas in the tube.

- not all identical, unlike electrons. - of mass or e/m ratio varying with the gas used.

On the measurements of e/m ratio for different gases, and assuming that they all have the same charge on the various ions, the hydrogen ion was discovered to be the smallest possible positive ion. Hence, the hydrogen ion was believed to be a fundamental particle of matter, and was called the proton.

The proton has the following properties:

- it is a positively charged particle.

- its charge is equal to that of an electron, but opposite in sign.

- it’s mass is 1.0073 amu, which is approximately 1840 times greater than that of an electron.



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