Rutherford conducted an experiment where he fired alpha particles at a thin gold foil. Most alpha particles passed straight through the foil, but some were deflected at small angles and a few were deflected at large angles. This showed that the positive charge and mass of an atom must be concentrated in a small nucleus at the center, with electrons orbiting the outside. The Rutherford model concluded that (1) the positive charge of an atom is contained in a nucleus at its center, (2) there is mostly empty space between the nucleus and electrons, and (3) electrons revolve around the positively charged nucleus.

1. RUTHERFORD ATOM MODEL (ATOMIC STRUCTURE) by M.KANNAN

3. Alpha particles start Lead screen Thin gold foil Fluorescent screen EXPERIMENT

4. DESCRIPTION Alpha particles from the polonium sample passed through lead slit for a narrow beam. Then they passed through thin gold foil.A t the centre of the fluorescent screen more scintillations were observed .some were observed little above and few further above as it is shown in the figure. Rutherford told positive charge of atom should be contained at the centre of the atom;only then repulsive force 2Ze*e/r Newtons (Z is atomic number, e is electron charge and r is radius of nucleus) could have deflected alpha particles.Deflection occurred because alpha particles too are positively charged.

5. THEORY The fact that more alpha particles went straight shows that there is more space between electrons and the positively charged nucleus. The angle of scattering depends upon the factor called ‘impact parameter.’ closer the approach of alpha particle more the de4flection was observed. The impact parameter is given by the factor,b= Ze*e* cot0.5 0 .5mv*v 4 where is angle of scattering,m is mass of alpha particle&v is its velocity.

6. DEFINITION FOR IMPACT PARAMETER Impact parameter(b) is the perpendicular distance between the velocity vector and centre of the nucleus. b

7. Conclusion 1 Positive charge of atom is contained at the core called nucleus.

8. CONCLUSION 2 There is more space between positively charged nucleus and negatively charged electrons.

9. CONCLUSION 3 The negatively charged electrons revolve around the positively charged nucleus.

10. SUMMARY Conclusions 1,2 &3 constitute Rutherford Atom Model.

11. EXERCISE Calculate angle of scattering if alpha particle retraces its path.

12. SOLUTION FOR EXERCISE b=Ze*ecot0.5 0.5mv*v   Here b= 0 so cot0.5  hence 0.5  and 

13. ALL THE BEST! GOD BLESS YOU,DEAR STUDENTS,AS YOU LEARN MORE OF HIS CREATION.