Question

How does Rutherford’s model of the atom explain why some of the alpha particles directed at the gold foil were deflected straight back towards the source?

Answer 1

Hint: Ernest Rutherford’s performed a gold foil experiment to determine the atomic structure and gave Rutherford's atomic structure. The atom contains a nucleus at its center which contains positively charged protons and neutral charged neutrons.

Complete step by step answer:
In 1905, Ernest Rutherford did an experiment where he tested the plum pudding model. His two students Hans Geiger and Ernest Marsden directed the beam of alpha particles at a thin gold foil in a vacuum.
The following observation was made
(1) Most of the alpha particles pass straight through the gold foil.
(2) A small number of alpha particles get deflected back by the angles greater than 4 degree as they pass through the golf foil.
(3) A very small number of alpha particles came back after hitting the gold foil.
The particles which passed straight through the gold foil were the alpha particles which were positively charged.
The few alpha particles which were deflected back as they were repelled by the nuclei which are also positively charged.
From the following observation, he concluded that
(1) The most of the alpha particles passed straight to the foil shows that in atoms most of the space is empty.
(2) A small number of alpha particles which were deflected at large angles shows that there is a positive charge concentrated in the atom. Like charges repel each other by this fact the positive alpha particles were repelled by positive charges.
(3) The very small number of alpha particles went straight back shows that the positive charge and mass are concentrated in a small space in the nucleus of the atom.

Note:
You must know that the experiment was performed in the vacuum because the deflection of the alpha particles would only take place due to collision with the gold foil and not due to collision with air particles. Gold was used as it can be rolled out very thin without cracking.