4.0 Rutherford Model of Atom

  Structure of Atom

• Ernest Rutherford performed an experiment called ‘Gold Foil Experiment’ or $\alpha $- ray scattering experiment’ to test the structure of an atom as proposed by Thomson.
  
• He expected that the alpha ($\alpha $) particles would just pass straight through the gold foil and could be detected by a photographic plate
• A stream of high energy $\alpha$ -particles from a radioactive source was directed at a thin foil(thickness~100 $nm$) of gold metal.
• The thin gold foil had a circular fluorescent zinc sulphide screen around it. When $\alpha $-particles struck the screen, a tiny flash of light was produced at that point.

It was observed that :

• most of the $\alpha $– particles passed through the gold foil undeflected.
• a small fraction of the $\alpha $–particles was deflected by small angles.
• a very few $\alpha $– particles (~1 in 20,000) bounced back, that is, were deflected by nearly 180°.

Conclusion

• The atom contained some dense and positively charged region located at the center of the atom that is called as nucleus.
• All the positive charge of the atom and most of its mass was contained in the nucleus.
• The rest of the atom must be empty space which contains the much smaller and negatively charged electrons.