ATOMIC THEORY

CONTENT

1. Gross Features of the Atom
2. J. J. Thompson’s Cathode Rays Experiment
3. Bohr’s Model of the Atom
4. Energy Levels  and Maximum Number of  Electrons
5. Line Series in the Hydrogen Spectrum
6. Outline Description of the Rutherford’s Alpha Scattering Experiment

Gross Features of the Atom

J.J. Thompson’s Cathode Rays Experiment

Experiments on discharge tubes performed by J. J. Thomson (1897) led to the discovery of the electron (cathode ray) as a subatomic particle.

Cathode rays:

1. move in a straight line normal to the cathode and can cast the shadow of an object placed along their path.
2. possess kinetic energy and so can cause the motion of a mechanical paddle wheel placed along their path.
3. attract positive charge and repel negative charge, indicating that they are negatively charged.
4. have a constant value of 1.76 × 10¹¹  coulomb kg⁻¹ for the charge-to-mass ratio (^e/_m)  no matter the gas used in the tube or the nature of the materials of the electrodes and the tube.