Question

Explain how a particle scattering experiment led Rutherford to estimate the site of the nucleus.

Answer 1

Hint: Firstly, we need to know the characteristics of alpha rays. Then explain Rutherford’s scattering experiment and understand the result of the experiment. From this, we can interpret how Rutherford’s alpha ray scattering experiment led to the estimation of the site of the nucleus.

Complete answer:
Alpha rays are used in Rutherford’s alpha ray scattering experiment. Alpha rays are a beam of positively charged particles. These particles have two protons and one neutron.
In Rutherford’s alpha ray scattering experiment, the alpha rays are incident on a very thin gold foil. It was observed that many alpha particles passed through the gold foil but one out of every 20,000 reflected back at small angles.

So, Rutherford made a few conclusions from the observations. They are-
a. As many of the rays are going the foil undeflected most of the atom must be hollow.
b. Few rays coming out were highly deflected, indicating the presence of positive charge and that it occupied a very little volume of the atom.
c. After many calculations, Rutherford found that the size of the nucleus was 105 times smaller than the atom.

Based on this, Rutherford put forth the nuclear model of an atom. It states that-
a. The positive region of the atom was very small and most of the mass of the atom was concentrated in this region. It was called the nucleus.
b. The electrons revolve around the nucleus in well-defined paths called orbits.
c. The electrons and nucleus are held together by the electrostatic force of attraction.
This is how the alpha ray scattering experiment of Rutherford led to the estimation of the site of the nucleus.

Note:
Many people confuse alpha particles for helium atoms. It is not true. We assume it to be so, for our convenience. Before Rutherford’s nuclear model, the plum pudding model of the atom proposed by J. J. Thomson was accepted. In this model, the positive and negative charges were evenly spread as in a melon. But if this were true, the rays must only deflect slightly as they pass through. But this is not the case.