Question

Rutherford's experiment, which established the nuclear model of the atom, used a beam of: (a) \(\beta\) -particles, which impinged on a metal foil and got absorbed. (b) \(\gamma\) -rays, which impinged on a metal foil and ejected electrons. (c) Helium atoms, which impinged on a metal foil and got scattered. (d) Helium nuclei, which impinged on a metal foil and got scatterd.

Short answer

(d) Helium nuclei, which impinged on a metal foil and got scattered.

Step-by-step solution

Understanding Rutherford's Experiment

Rutherford's experiment, also known as the gold foil experiment, was a landmark study in physics that led to the proposal of the nuclear model of the atom. In this experiment, Rutherford directed a stream of particles at a thin foil of metal to observe how they would scatter, helping to determine the structure of the atom.

Identify the Particles Used

The key to answering this question lies in knowing what type of particles were used in Rutherford's experiment. Rutherford used a source that emitted alpha particles to bombard the metal foil. Alpha particles are essentially helium nuclei, which consist of two protons and two neutrons.

Analyze the Options

Consider each option provided in the exercise and match it to the historical context of Rutherford's experiment: (a) b2-particles are a form of radiation but were not used in this experiment. (b) b3-rays are electromagnetic radiation and are not relevant to Rutherford's method. (c) Helium atoms contain electrons, which were not what Rutherford used. (d) Helium nuclei match the description of alpha particles used in trying to determine the atomic structure.

Select the Correct Option

Based on the analysis of the options, the correct choice is the one that identifies helium nuclei as the particles used in the experiment. These nuclei are responsible for the scattering effect observed by Rutherford, which provided insight into the structure of the atom, specifically the concentration of positive charge in a small nucleus.

Key concepts

Nuclear Model of the Atom

The nuclear model of the atom was famously established by Ernest Rutherford through his gold foil experiment in 1909. Before this pivotal study, J.J. Thomson's plum pudding model was the accepted theory, where an atom was thought to be a uniform sphere of positive charge with electrons embedded within it, much like raisins in a pudding. However, Rutherford's findings challenged this idea by demonstrating that the positive charge in an atom is not diffused but rather concentrated in a small, dense core.

Rutherford proposed that most of the mass of the atom and all of its positive charge are concentrated in a tiny core called the nucleus. This nucleus is surrounded by electrons that orbit it much like planets around the sun, leading to the understanding that an atom is mostly empty space. This was a groundbreaking shift in atomic theory, paving the way for future models and discoveries in atomic physics.

Alpha Particles

Alpha particles play a crucial role in Rutherford’s gold foil experiment. These particles are essentially helium nuclei, made up of two protons and two neutrons. Due to their relatively high mass and positive charge, alpha particles serve as excellent projectiles for probing the internal structure of atoms.

In Rutherford’s experiment, alpha particles were emitted from a radioactive source and directed at a thin sheet of gold foil. The expectation was that these heavy particles would pass through the foil with minimal deflection if Thomson's plum pudding model was correct. However, while most of the particles passed through with little or no deflection, some were scattered at large angles, and a very few even rebounded back towards the source.

This unexpected outcome indicated that these alpha particles were encountering a very concentrated positive charge within the atom—a discovery that was instrumental in identifying the presence of the atomic nucleus.

Atomic Structure Determination

Determining atomic structure is a fundamental aspect of understanding matter. Rutherford's gold foil experiment was critical in redefining these structural properties at the atomic level. Prior to his work, the internal organization of atoms was largely misunderstood.

Through meticulous observation of the scattering patterns of alpha particles, Rutherford provided concrete evidence of a compact nucleus containing most of the atom's mass and positive charge. The discovery that some alpha particles were deflected at wide angles suggested the existence of a dense center within the atom.

This discovery led to the conclusion that atoms are primarily empty space, with a small nucleus at the center and electrons orbiting around it in various levels. As a result, Rutherford's insights laid the groundwork for the Bohr model and later advancements in quantum mechanics, profoundly shaping our understanding of atomic and molecular chemistry.