2. (a) Which experiment established the presence of atomic nucleus? What features of the nucleus were
deduced from this experiment?
(b) What are the drawbacks of Rutherford's model of atom?
Answers
Explanation:
Objective:
To demonstrate the scattering of alpha particles by gold foil.
Background:
Model for the structure of an atom had been first proposed by J.J. Thomson. Later, followed many theories however, Rutherford's model was finally accepted as the correct nuclear model. Rutherford had shown his model with help of an experiment.
Rutherford's scattering experiment:
Rutherford's model of an atom :
Ernest Rutherford was interested in knowing how the electrons are arranged within an atom. Rutherford designed an experiment for this. In this experiment, fast moving alpha (α)-particles were made to fall on a thin gold foil.
He selected a gold foil because he wanted as thin a layer as possible. This gold foil was about 1000 atoms thick.
α-particles are doubly-charged helium ions. Since they have a mass of 4µ, the fast-moving α-particles have a considerable amount of energy.
It was expected that α-particles would be deflected by the sub-atomic particles in the gold atoms. Since the α-particles were much heavier than the protons, he did not expect to see large deflections. But, the α-particle scattering experiment gave totally unexpected results .
Observations of Rutherford's scattering experiment:
As we can see in Fig. 1.
Most of the fast moving α-particles passed straight through the gold foil.
Some of the α-particles were deflected by the foil by small angles.
Surprisingly one out of every 12,000 alpha particles appeared to rebound.