Priyam Study Centre

A Page about Chemistry and Related Topics.

Jul 15, 2018

Discovery of electron,Proton,Neutron


Discovery of electron: 

Experiment of William Crooks in 1878: Under normal condition a gases poor conductor of electricity. At reduced pressure however conduction occur when the discharge tube are partially evaluated and connected a high voltage spark coil electric current flow through it . This flow of electricity is associated with the glow of rays of light which has their origin in cathode surface.
Thomson shows that these rays could be bent from their path both by electric field & magnetic field & hence the rays must be carrying positively charged particles. He could prove from the direction of bending that the cathode rays were made up by negatively charged particles. These rays are called electrons.

Discovery of Proton: 

Since the extra nuclear electrons contributes negatively charged particles with negligible mass of the atom and since atom is electrically neutral it follows that the nucleus must be carry particles which will account both the mass & the positive charged of the atom.

In this discharge tube perforated cathode is used. When high voltage electric current applied to the discharge tube at very low pressure 0.01mm. In 1907 J.J Thomson named it positive Rays.

Discovery of Neutron: 

According to atomic weight Scale mass of atom = Mass of proton in an atom. But it is only satisfied for hydrogen atom and carbon atom. In 1930 Bothe & Becker, when alpha particles were made to strike on beryllium target there appear some type of radiations. This ray does not deflected by electric or magnetic field. This incident shows that these particles are neutral. In 1932 Chadwick named these particles as neutron.