Problem 25 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Rurtherford'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 scattered

Step-by-Step Solution

Answer

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

Step 1: Understand the Context

Rutherford's experiment, specifically the gold foil experiment, was pivotal in establishing the nuclear model of the atom. During this experiment, particles were directed at a thin sheet of metal to observe their scattering, which helped improve the understanding of atomic structure.

Step 2: Analyze the Options

Evaluate each provided option: (a) \(\beta\)-particles - These are electrons and do not fit the context of Rutherford's experiment. (b) \(\gamma\)-rays - These are electromagnetic radiation and not used in this experiment. (c) Helium atoms - These are neutral and wouldn't interact in the way observed. (d) Helium nuclei - Known as alpha particles, these positively charged particles were used in the experiment.

Step 3: Choose the Correct Particle

In Rutherford's experiment, he used alpha particles (helium nuclei) to be directed at the gold foil. These particles are positively charged and observed scattering due to the presence of a dense nucleus in the atom.

Step 4: Confirm the Conclusion

Option (d) helium nuclei, which impinged on the metal foil and got scattered, matches historical accounts of Rutherford's experiment, leading to the establishment of the nuclear model of the atom, where most of the atom's mass concentrates in the central nucleus.

Key Concepts

nuclear model of the atom

In the early 20th century, the understanding of the atom shifted dramatically thanks to Rutherford's experiment. Before his breakthrough, the plum pudding model, proposed by J.J. Thomson, was widely accepted. This model suggested that positive charge was spread out evenly with electrons embedded throughout, like plums in pudding.

Rutherford's gold foil experiment refuted this by revealing the existence of a small, dense core within the atom: the nucleus. He discovered that most of the atom is empty space with a central nucleus that contains most of the atomic mass and exhibits positive charge. This discovery marked the cornerstone for the nuclear model of the atom. Key features of this model include:

• A small, dense nucleus containing protons and, subsequently discovered, neutrons.
• The rest of the atom is mostly empty space.
• Electrons orbit this central nucleus.

The nuclear model serves as the foundation for modern atomic theory.

alpha particles

Alpha particles played a crucial role in Rutherford's gold foil experiment. These particles are essentially helium nuclei, comprising two protons and two neutrons, and carry a positive charge. Their use was vital because their positive charge could interact with the nucleus, which also held a positive charge.

Alpha particles are relatively heavy and can cause dense deflections due to interactions with the equally positively charged nuclei of atoms. Importantly, their behavior in Rutherford's experiment demonstrated that atoms are not as solid as once thought.

When Rutherford directed alpha particles at the thin gold foil, he observed that while most particles passed through with no deflection, a few were deflected at sharp angles. This observation signified that the nucleus is dense enough to repel the alpha particles, proving the existence of a concentrated core inside the atom.

gold foil experiment

The gold foil experiment was a landmark scientific endeavor conducted by Ernest Rutherford in 1909. During this experiment, Rutherford and his team aimed to explore the atomic structure by firing alpha particles at a very thin sheet of gold foil—a mere few atoms thick.

Key observations from the experiment included:

• Most alpha particles passed straight through the foil, indicating that atoms' composition is predominantly empty space.
• Some alpha particles deflected at minor angles, and a few even bounced straight back, suggesting there is a concentrated positive charge within the atom, now known as the nucleus.

From these observations, Rutherford concluded that contrary to the plum pudding model, atoms have a small, dense nucleus, leading to the formulation of the nuclear model of the atom. This experiment not only corrected misconceptions but also paved the way for future discoveries in atomic physics.