Electrons were discovered by J.J. Thomson in 1897.
J. Thomson’s experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons.
He performed an experiment on the cathode rays and showed that these are charged particles.
The velocity of cathode rays was much less as compared to the speed of light.
So, to measure the charge to mass ratio of cathode rays, he devised new ways.
Thompson therefore concluded that the cathode rays are 11000th mass of hydrogen ion (which is a proton). The negatively charged cathode ray particles came to be known as electrons which have negligible mass.
Characteristics of an Electron
Mass of an Electron:
Charge of an Electron:
DISCOVERY OF PROTON
The existence of proton in the atoms was shown by E. Goldstein in 1886.
When Goldstein passed electricity at high voltage through a gas at very low pressure taken in a discharge tube, streams of heavy particles were given out by the anode (positive electrode).
These streams of particles are called anode rays.
The anode rays obtained from hydrogen consist of protons.
A proton can be produced when we remove an electron from the hydrogen atom.
He also found that the charge to mass ratio of the positive particles depend on the nature of the gas present in the discharge tube.
So, the charge to mass ratio (e/m) was different for different gases.
It was highest in case of the hydrogen gas mainly because hydrogen is the lightest atom meaning m will be the least hence e/m ratio will be highest in this case.
The proton is a positively charged particle found in the atoms of all the elements.
Protons reside inside neutron.
Characteristics of a Proton:
Mass of a Proton: The relative mass of a proton is 1 u.
Charge of a Proton: The charge of a proton is equal and opposite to the charge of an electron. The absolute charge of a proton is
coulomb of positive charge.
DISCOVERY OF NEUTRON
The discovery of another subatomic particle by James Chadwick in 1932.
This particle is called neutron.
The neutron is a neutral particle found in the nucleus of an atom.
Characteristics of a neutron:
Mass of a Neutron: The relative mass of a neutron is 1 u.