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Here's a detailed explanation of the discovery of electrons, protons, and neutrons, aligned with the Class 11 NCERT textbook

 


       



Electron Discovery


1. J.J. Thomson's Experiment (1897): Thomson investigated cathode rays using a cathode ray tube.

2. Cathode Ray Tube: A vacuum tube with electrodes at both ends, where electricity passes through.

3. Observations:

    - Cathode rays were deflected by electric and magnetic fields.

    - Deflection indicated a negatively charged particle.

    - Charge-to-mass ratio was calculated.

4. Conclusion: Electrons are negatively charged particles with:

    - Charge: -1.602 x 10^-19 C

    - Mass: 9.109 x 10^-31 kg

    - Charge-to-mass ratio: 1.759 x 10^11 C/kg


Proton Discovery


1. Ernest Rutherford's Gold Foil Experiment (1919): Rutherford bombarded gold foil with alpha particles.

2. Gold Foil Experiment:

    - Alpha particles scattered by gold foil indicated a dense, positively charged nucleus.

    - Scattering pattern revealed the nucleus's size and charge.

3. Observations:

    - Alpha particles scattered at large angles.

    - Scattering indicated a small, dense nucleus.

4. Conclusion: Protons are positively charged particles with:

    - Charge: +1.602 x 10^-19 C

    - Mass: 1.673 x 10^-27 kg


Neutron Discovery


1. James Chadwick's Experiment (1932): Chadwick bombarded beryllium with alpha particles.

2. Neutron Experiment:

    - Beryllium emitted neutral radiation when bombarded with alpha particles.

    - Neutral particles had a mass slightly larger than protons.

3. Observations:

    - Neutral particles detected.

    - Mass calculated.

4. Conclusion: Neutrons have:

    - No charge.

    - Mass: 1.675 x 10^-27 kg.


Key Concepts 


1. Atomic Number (Z): Number of protons in an atom's nucleus.

2. Mass Number (A): Sum of protons and neutrons in an atom's nucleus.

3. Isotopes: Atoms with the same Z but different A.

4. Nuclear Stability: Depends on proton-neutron ratio.



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