Class 9 Chemistry Structure of The Atom Discovery of Electrons

Discovery of Electrons

  • The existence of electrons in atom was shown by J.Thomson in 1897.


  • Streams of particles were produced at cathode (negative electrode) when electricity is passed at a very high voltage.
  • As they originated at cathode so they were known as cathode rays.


  • Cathode rays consist of small, negatively charged particles called electrons.
  • Since all the gases form cathode rays, it was concluded that all the atoms contain negatively charged particles called electrons.
  • The electrons are negatively charged particles found in atoms of all elements.
  • Electrons are represented as e-.
  • The charge on electron is -1.6 x 10-19
  • The relative charge on electron is (-1).
  • The relative mass of electron = (1/1836) u and the absolute mass of electron is 9 x 10-28

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