Chapter 17, Problem 16A

To determine

To explain: The discovery of person R when his group bombarded a thin foil of gold with subatomic particles.

Answer to Problem 16A

The nucleus of an atom is discovered.

Explanation of Solution

Introduction:

Person Rand his group bombarded the thin gold foil with a subatomic particles say alpha particles and performed an alpha particle scattering experiment. The entire experiment was carried out in a vacuum. The source of alpha particles and the gold foil were surrounded by a screen that was coated with a layer of zinc sulphide. It was expected that entire alpha particles that strikes on the gold foil would pass through the gold foil. But the result was not as they expected. Instead some of the alpha particles reflected back from the foil which was recognized from the glowing spot on the surrounded screen. This experiment leads to the discovery of the nucleus.

From the alpha particle scattering experiment Rutherford concluded that,

• Major part of the alpha particles that strikes on the gold foil passed through the foil without getting any deviation in its path. This indicates that the major portion of the atom is unfilled.
It was noticed that a very small number of alpha particles gets deflection from the foil at an angle of ${90}^0$
• or even more angles. Since alpha particles are positively charged there must be a positively charged center inside the atom to deflect the alpha particles. This core in the atom is called by the name nucleus.
• As only a small part of the incident alpha particles gets deflection from the foil, it was concluded that the nucleus of an atom occupies a very small volume compared to that of whole atom.
• Since the nucleus deflects the alpha particles which has considerable mass, it was concluded nucleus of an atom encompasses almost entire mass of that atom..

Conclusion:

The bombardment of a thin foil of gold with subatomic particles by person R and his group leads to the discovery of atomic nucleus.