Question

What conclusion was drawn by Rutherford based on Geiger-Marsden's experiment on scattering of alpha particles.

Answer 1

Hint-The experiment studied the extent to which alpha particles were scattered after passing through a thin gold foil. The result was that most of the particles passed undeflected while some suffered scattering and very few suffered scattering through a large angle up to 90 degree. Rutherford gave an explanation for this result by suggesting the nuclear model of atoms.

Complete step by step solution:
In the Geiger-Marsden's experiment a thin gold foil was placed at the centre of a rotatable detector made of zinc sulfide. Then a beam of Alpha particles was allowed to fall on the foil and scattered alpha particles were analyzed.

The result of the analysis was that most of the alpha particles passed undeflected. Some of the particles were scattered by more than one degree. Very few particles were deflected by more than 90 degrees.
From the observations of this experiment Rutherford concluded that in order to deflect the positively charged alpha particles there must be a repelling force. Since most of the particles passed undeflected he concluded that this positive charge is concentrated in the centre and the rest of the space of atoms is almost empty. So, if the alpha particle passes through the centre it will get deflected more and if it passes through the other free area in the atom it will pass undeflected. Thus, he suggested the nuclear model of an atom in which the entire positive charge and most of the mass is concentrated at the centre of the atom. This is called the nucleus of the atom. The size of the nucleus is between ${10^{ - 15}}\,m$ to ${10^{ - 14}}\,m$ . The rest of the space in the atom is mostly empty. The alpha particle coming close to the nucleus will be scattered at large angles. When there is a head on collision then it will bounce back.

Note:The electrons in the atom have no significant effect on the deflection of alpha particles. This is because the mass of the electron is negligible compared to the mass of the nucleus. They will not affect the incident alpha particle trajectory.