Discovery of Protons: Model, Discovery, and Experiment

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What are Protons?

The three different sub-atomic particles present in the nuclei of an atom are called, protons, neutrons, and electrons and they were discovered in the nineteenth and twentieth century.

Discovery of Protons

The nucleus of the atom was discovered by a scientist named Ernest Rutherford in the year 1911 in his well-known gold foil experiment. He stated that all the positively charged particles present in an atom were concentrated in a singular core and that maximum of the atom’s volume was empty.

He also stated that the total number of positively charged particles present in the nucleus of an atom is always equal to the total number of negatively charged electrons present around it.

The finding of the proton is credited to Ernest Rutherford, who showed that the nucleus of the hydrogen atom (that is a proton) is present in the nuclei of all atoms in the year 1917. But, the presence of a positively charged particle found in an atom had been first noticed by E. Goldstein in the year 1886 based on the concept that atoms are generally electrically neutral which means that they have the same number of positive and negative charges.

He performed a series of experiments and detected that when high voltage electricity was passed through a cathode tube which was fitted with a perforated cathode (pierced disk) and thus contained gas at low pressure then a new type of ray was produced from a positive electrode or commonly called as the anode which moved towards the cathode.

These new rays he named as canal rays, positive rays, or anode rays. Further, the canal Ray experiment is the experiment that was performed by German scientist Eugen Goldsteinin that led to the discovery of the proton. The discovery of proton occurred after the discovery of the electron which further supported the structure of the atom.

The Canal Ray Experiment

• The apparatus as shown above in the figure is set by providing a very high voltage source and emptying the air to preserve low pressure inside the tube.

• High voltage is thus passed to the two metal pieces as shown to ionize the air and hence making it a conductor of electricity.

• The electricity started to flow as the circuit completes.

• When the voltage was increased further to several thousand volts, then a faint luminous ray was observed extending from the holes in the back of the cathode.

• The rays thus observed were moving in the opposite direction of cathode rays and were termed as canal rays.

Conclusion of Canal Ray Experiments

• As compared to cathode rays, canal rays depend upon the nature of gas present in that tube. It is because of the fact that the canal rays consisted of positive ionized ions which were formed by the ionization of gas present in the tube.

• The behavior of particles present in an electric and magnetic field was thus the opposite to that of cathode rays.

Protons Characteristic

Protons are referred to as the positively charged subatomic particles of an atom. It is represented by the symbol p or p+.

A hydrogen atom comprises of one proton and one electron, so when an electron is removed from the hydrogen atom then a proton is produced. This is the reason why the proton is also represented as H+.

It thus possesses +1e (or 1.60 10-19 coulomb) positive electric charge.

The word Proton is a Greek word that means ‘First’. It was initially used by Ernest Rutherford in the year 1920. The subatomic particles protons and neutrons are collectively known as nucleons.

What is The Mass of Protons?

The mass of the proton is 1.67 10-24 gram or 1.67 10-27 kg.

The mass of an electron is equal to 9.1 10-28 consequently the mass of a proton is 1836 times the mass of an electron. Though the mass of a proton is almost always equal to the mass of a neutron present in the nuclei of an atom.

The number of protons present inside the nucleus of an atom is always equal to the atomic number (Z) of the atom.


Number of Protons = Atomic Number

For instance, the atomic number of the Krypton (Kr) atom is equal to 36. Henceforth, the nucleus of the Krypton atom consists of 36 protons.

Properties of Protons / Positive Rays / Anode Rays

1. They are positively charged ions.

2. They travel in straight lines and thus can cast a shadow of the thing located in their path.

3. These positive rays are also deflected by electric as well as a magnetic field.

4. Mass of proton is equal to 1.672 x 10-24 g.

5. The charge on the proton is equal to +1.602 x 10-19 coulombs.

Protons Citations


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