Rutherford’s gold foil experiment | Electronic structure of atoms | Chemistry | Khan Academy

Summary

This video explores Ernest Rutherford's groundbreaking experiment, where he shot alpha particles at a thin gold foil to investigate the structure of the atom. Initially expecting the particles to pass through based on the plum pudding model, Rutherford was stunned when a small fraction bounced back. This led him to propose a new atomic model, revealing the existence of a tiny, dense, positively charged nucleus at the center of the atom, surrounded by mostly empty space. Rutherford’s discovery paved the way for modern atomic theory, explaining atomic structure in a way that reshaped scientific understanding.

Takeaways

• 😀 Rutherford's experiment involved shooting alpha particles at gold foil to study the structure of the atom.
• 😀 Alpha particles are helium nuclei with two protons and two neutrons, and no electrons, giving them a 2+ charge.
• 😀 Rutherford used radium in a lead box to direct alpha particles through a small hole at gold foil.
• 😀 The plum pudding model, proposed by J.J. Thomson, was the prevailing atomic model at the time of Rutherford's experiment.
• 😀 The plum pudding model suggested that electrons were scattered within a positively charged 'soup' in an atom.
• 😀 Based on the plum pudding model, Rutherford predicted that most alpha particles would pass straight through the gold foil.
• 😀 Rutherford observed that most alpha particles did indeed pass through the foil, but a small fraction were deflected or bounced back.
• 😀 Around 1 in 20,000 alpha particles were deflected back, an unexpected result that led Rutherford to recheck his experiment.
• 😀 The unexpected bouncing back of alpha particles suggested a tiny, massive, and positively charged nucleus at the center of the atom.
• 😀 Rutherford proposed a new atomic model, known as the Nuclear Model, where the atom is mostly empty space, with a tiny, dense, positively charged nucleus at the center.

Q & A

What was Rutherford's primary goal in conducting the gold foil experiment?

Rutherford aimed to learn more about the structure of the atom by shooting alpha particles at a thin sheet of gold foil to see how they interacted, with hopes of validating the plum pudding model of the atom.

What is the plum pudding model of the atom, and who proposed it?

The plum pudding model, proposed by J.J. Thomson, suggests that the atom consists of small, negatively charged electrons scattered throughout a positively charged 'soup' that neutralizes the negative charge.

What are alpha particles, and what was their role in Rutherford's experiment?

Alpha particles are positively charged particles composed of two protons and two neutrons (He2+ nuclei). In Rutherford's experiment, they were fired at gold foil to study how atoms interact with subatomic particles.

Why did Rutherford expect most of the alpha particles to pass straight through the gold foil?

Rutherford expected most alpha particles to pass straight through because, according to the plum pudding model, the atom's positive charge was spread out weakly across the atom, not concentrated in any small region.

What surprising result did Rutherford observe during the experiment?

Rutherford observed that a tiny fraction of the alpha particles (about 1 in 20,000) bounced back from the gold foil, which was unexpected and led to a reconsideration of the atomic structure.

How did Rutherford explain the deflection and reflection of alpha particles?

Rutherford explained that the deflection and reflection of alpha particles occurred because they encountered a very small, dense, positively charged nucleus at the center of the atom, which repelled the alpha particles.

What did Rutherford's experiment reveal about the size of the atomic nucleus?

Rutherford calculated that the nucleus was extremely small, about 1/10,000 of the atom's volume, based on how few alpha particles interacted with it.

What is the nuclear model of the atom, and how is it different from the plum pudding model?

The nuclear model, proposed by Rutherford, suggests that the atom has a tiny, dense, positively charged nucleus surrounded by electrons. This contrasts with the plum pudding model, which placed electrons in a spread-out positive 'soup'.

What was the significance of Rutherford's new model for atomic structure?

Rutherford's nuclear model revolutionized the understanding of atomic structure by introducing the idea of a central nucleus, leading to further advancements in atomic theory and the eventual development of modern atomic models.

What was left unresolved in Rutherford's model, and how did future experiments address these gaps?

Rutherford's model did not fully explain the behavior of electrons, such as their arrangement or motion. Future experiments and theories, including Bohr's model, provided answers to these unresolved questions.