Question

Rutherford’s experiment on scattering of alpha particles proved that:

Answer 1

An alpha particle is a positively charged particle made up of two protons and two neutrons. It has a$+2$ charge and the symbol for an alpha particle is ${{_{2}}^{4}}He$. They are emitted by a radioactive substance.

Complete answer:
Let us understand the details of this experiment, the setup consisted of a lead box (with a hole)containing a radioactive substance rich in alpha particles, thin gold foil, a circular screen coated with zinc sulphide surrounding the foil.

Alpha particles emitted from the source were bombarded at the gold foil and particles got scattered in different directions. Their scattering pattern was shown by the circular screen placed around the foil. The particles leaving the foil,when striked on the circular screen produced a tiny glowing flash.

It was observed that most alpha particles remain undeflected, that is, they continued in the straight path as if the gold foil was absent and only a few of them showed deflection which was very small. A very few of them essentially $1$ in $12000$ rebounded back. It led to significant conclusions which are:
-As most of the particles passed undeflected, Rutherford concluded that most of the space inside the gold atom was empty.

-A few particles were deflected from their path by small angles indicating that there must be a positively charged centre which was repelling alpha particles. As these particles were few in number, this led to the conclusion that a positively charged centre occupies a tiny space.

-Few particles that are rebounded back indicate that all the positive charge of the atom was concentrated in a very small volume in the centre. Rutherford named this positive centre of the atom as nucleus.

-Looking at the proportion of the particles undeflected, deflected and rebounded and based upon some calculations. He concluded that most of the mass of the atom is concentrated in its nucleus. Therefore, he was the one to show that the atom has a nucleus.

Note: Rutherford’s model of atom was also known as the planetary model of atom as the nucleus of the atom can be compared to the sun and the electrons revolving around the nucleus can be compared to the planets revolving around the sun.