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Sub-Atomic Particles

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Sub-Atomic Particles - Lesson Summary

Any substance that has mass and occupies space is called matter. It is made up of small particles called atoms and molecules that cannot be further divided.

Dalton proposed that atom is the ultimate particle of matter proposed a theory, called Dalton's atomic theory.

Dalton's atomic theory was able to explain the laws of chemical combination, conservation of mass, multiple proportion and constant composition.

It could not explain the electric nature of matter as explained by Michael Faraday.

Michael Faraday found that when electricity is passed through an electrolyte, which is a solution that conducts electricity, chemical reactions resulting in the deposition of matter at the electrodes.

Cathode rays were discovered in 1897 by J.J. Thomson and other scientists through a series of experiments. He proposed that the cathode rays consisted of negatively charged particles, named as electrons.

Thomson also concluded that the properties of cathode rays do not depend upon the material of electrodes and the nature of the gas present in the cathode ray tube.

To calculate the charge of an electron, Millikan conducted the famous Oil Drop Experiment.

Millikan calculated the charge on an electron to be 1.6 × 10-19 coulombs.

Similar to discovery of cathode rays let to the discovery of the negative particles called electrons, the discovery of anode rays led to the discovery of the positive particles called protons.

Anode rays also called canal rays, were discovered by E. Goldstein in 1886.

By 1913, it was determined that the atomic number of an element is equal to the number of protons present in its nucleus.

It was discovered that the mass of all protons in an atom put together is much less than the actual mass of an atom. It was thus concluded that the excess mass was due to some other particle present in an atom that had considerable mass but no charge.

In 1932, James Chadwick proved the presence of heavy, neutral particles through a series of scattering experiments. From his experiments, Chadwick observed the emission of a neutral particle whose mass was equivalent to that of a proton named this particle as neutron.

After all the sub-atomic particles were discovered, it was concluded that an atom is made up of Protons or positively charged particles, Electrons or negatively charged particles and Neutrons are neutral particles.

In addition to electrons, protons, and electrons, there are some uncommon sub-atomic particles including positrons, neutrinos and antineutrinos, mesons, photons, gravitons and antiprotons are present inside the atom.

Following table gives charge, mass of the fundamental particles of the atom.

properties of Fundamental Particles

Name         Electron         Proton         Neutron Symbol  0  p  n Absolute charge  -1.6022x10 -19  +1.6022x10 -19  0 Relative charge  -1  +1  0 Mass/kg  9.10939x10 -31  1.67262x10 -27  1.67493x10 -27 Mass/u  0.00054  1.00727  1.00867 Approx mass/u  0  1  1


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