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Discovery of Electron Proton Neutron





The Greek philosopher Democrtius purposed that all matter consists of small indivisible particles which are called as atomos i.e. un-cuttable or indivisible.  
However by the end of 19th century, it was discovered that atoms consist of three fundamental sub-atomic particles; electrons, protons and neutrons.

Out of these sub-atomic particles; electrons were first discovered by Sir John Joseph Thomson (J.J. Thomson) in 1897 on the basis of study of cathode rays by Micheal Faraday in 1832. 
He observed that when electricity was passed through an electrolyte, it gets decomposed into elementary substances and this decomposition is called as electrolysis.

Further the same concept was used by Julius plucker in 1859 during the experiments with gas discharge tube. 
Later in 1870, Sir William Crookes, the English chemist and physicist developed the first cathode ray tube with a high vacuum. It was a long glass tube with metal electrodes on either ends and connected to a vacuum pump for controlling the pressure of gas inside the tube. 
  
At 1 atm pressure, there were no electric current flows through the tube. 
As the pressure reduced to 0.01 atm and a potential difference of about 10000 volts was applied to the electrodes, an electric current flows and light was emitted by the gas. 
This observation proved that some radiations are emitted from cathode and called as cathode rays.

Since these rays flow from cathode to anode, therefore they must have negative charge. 
Cathode rays travel in straight line from cathode to anode and consist of material particles as the wheel placed in the path of rays starts rotating. 
These particles were named as electrons by J.J. Thomson.  
He determined the charge by mass ratio of electrons by deflection of cathode rays under the simultaneous application of electric and magnetic field.

The value of e/m ratio was found to be 1.758820 x 108 Cg-1
This charge by mass ratio for the cathode ray particles was found to be exactly same not taking into account the nature of cathode or the nature of gas taken inside the discharge tube, and eventually showing that the electrons are the basic constituent of all  atoms. 
                                            
In 1886, Eugen Goldstein discovered the existence of a new type of rays in discharge tube and named as anode rays or canal rays. 
He observed these rays behind cathode on passing the electric discharge at low pressure.

Canal or anode rays also travel in straight line and are deflected by electric field towards cathode which proves that they are composed of positively charged particles. 
The charge by mass ratio of these particles depends upon nature of gas taken in discharge tube.

 It observed that the e/m ratio is least with hydrogen gas in discharge tube that is 9.58 x 104 cg-1.  
These lightest positively charged particles were named and characterised as protons by Ernest Rutherford in 1919 who purposed Rutherford model for atom to explain the atomic structure. 
This model proved that the mass of atom is concentrated in nucleus which contains protons. 
But there is one more particle in nucleus named as neutron by James Chadwick in 1932. 
He observed these particles during the bombardment of alpha particles on a thin film of Beryllium as highly penetrating neutral particles.

4Be9 + 2He4  --> 6C12 + 0n1

Some other Sub- Atomic Particles:
Neutrino were discovered in 1927 and it was pauli postulated a particle having zero mass and zero charge. 
Fermi then named it as neutrino but it was around 9n 1952, Allen and Rodeback successfully demonstrated the fee existence of neutrino.

Anti-Neutrino were discovered by Fermi and he indicated that these actually exist and was identified to have identical properties of neutrino but with a oppsite spin and according to fermi neutron decays to form 0n1 ---> 1H1 + -1e0 + neutrino / anitneutrino

Anti-Proton were discovered by Segre in 1955 at University of California produced this particle by bombarding copper target with accelerated protons. 
This particles mass and spin are exactly identicle with proton but the only difference that this particle has is its charge which is -1.

Anti-Electron or in other words the positron were discovered in 1932 by Anderson, a physicists and he found that the bombardment of Boron with an alpha particle resulted in the emission of this particle.

 Cork in 1956 discovered the anti-neutron and he found all the properties are identical to neutron with the exception of its spin which found to be neutron. 
These are produced when a proton strikes an anitproton which results in the production of the neutron and its anti particle antineutron.

Mesons are sub atomic particle having mass in-between to that of an electron and proton. 
These are agin of two different types namely π-meson and μ-mesons
These are also termed as pions and muons respectively.

Pions have mass compared to electron of 273 times and the charge could be negative or positive.

Muons in comparison to electron have mass 207 times and the charge could be either negative or positive.

The last of the mesons are termed as K-mesons and are almost 970 times that of electron in mass number and have a charge of either negative, positive or even zero.