Discovery of Protons

Introduction to discovery of protons:

John Dolton (1809) regarded the atom as a hard, dense and smallest indivisible particle of matter. However, the emission of negatively and positively charged particles from radioactive elements as well as from gases on passage of electricity through gases at very low pressures convinced the scientists that atoms is not indivisible but consists of much smaller fundamental particles. It is now fully established that atom consists of three major fundamental particles called electrons, protons and neutrons.

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discovery of protons


Electron was discovered in cathode ray experiment by J.J Thompson in 1887.

Electron is a negatively charged particle having a charged particle having a charge equal to 1.60206 x 10-9 C and a mass equal to 9.1091x 10-31 kg. Since the charge on the electron is the smallest charge of the electricity, it is usual to speak of the charge on an electron as unit negative charge. The mass of electron is 0.0005487 a.m.u.Proton:

Proton was discovered in anode ray experiment. proton mass = 1.67262158 × 10-27 kilograms. Its charge is same as electron but positive in sign.


It is neutral in nature and its specific charge is zero. It is heaviest among proton and electron.

atomic structure

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Discovery of Protons- Protons

It is a positively charged particle with charge, equal and opposite to that of electron and mass equal to 1.6727 x 10-27 kg. Thus, proton carries a unit positive charge and has a mass equal to 1.00728 a.m.u.

Discovery of protons – neutron: it is a neutral particle having mass equal to 1.6748 x 10-27 kg, thus, neutron carries no charge and has a mass equal to 1.00866 a.m.u.

Since, atom is electrically neutral; it consists of an equal number of electrons and protons

Discovery of Protons – Rutherford’s Nuclear Model of the Atom

Rutherford’s Nuclear Model of the Atom: According to Rutherford’s nuclear model:

An atom consists of a minute positively charged body located at its centre. It is known as nucleus. The nucleus though small, contains all the protons and neutrons. Since, the mass of an atom is almost entirely due to the presence of protons and neutrons; it is evident that almost the entire mass of an atom resides in the nucleus.

Discovery of protons – nucleus

The nucleus is surrounded by a suitable number of electrons, protons and neutrons revolving around it to balance the positive charge on the nucleus.

Most of the space between the nucleus and the revolving electrons in an atom is empty thus the centrifugal force arising from the circular motion of protons, neutrons and electrons which balances the force of electrostatic attraction between the nucleus and the electrons. The electrons do not fall into the nucleus.

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