Use Rutherford's gold-foil experiment to answer each of the following: (4.3) b. How did the results differ from what he expected?

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1. Rutherford expected that the alpha particles would pass through the gold foil with minimal deflection, based on the plum pudding model of the atom.
2. The plum pudding model suggested that the positive charge was spread out evenly throughout the atom, so the alpha particles would not encounter significant resistance.
3. However, the results showed that while most alpha particles passed through, some were deflected at large angles, and a few even bounced back.
4. This unexpected deflection indicated that the positive charge and most of the mass of the atom were concentrated in a small, dense region, which Rutherford called the nucleus.
5. The experiment led to the conclusion that the atom is mostly empty space, with a dense central nucleus, contradicting the plum pudding model.

Key Concepts

Rutherford's Gold-Foil Experiment

Rutherford's gold-foil experiment, conducted in 1909, involved firing alpha particles at a thin sheet of gold. The experiment aimed to probe the structure of the atom, leading to the discovery of the atomic nucleus. Most alpha particles passed through the foil, but a small fraction were deflected at large angles, indicating that atoms consist mostly of empty space with a dense, positively charged nucleus.

Expectations vs. Results

Rutherford initially expected that the alpha particles would pass through the gold foil with minimal deflection, based on the prevailing plum pudding model of the atom, which suggested a uniform distribution of positive charge. However, the significant deflections observed contradicted this model, leading to the conclusion that a concentrated positive charge exists in the nucleus, fundamentally altering the understanding of atomic structure.

Implications for Atomic Theory

The unexpected results of the gold-foil experiment had profound implications for atomic theory, leading to the nuclear model of the atom. This model posited that atoms have a small, dense nucleus surrounded by electrons, which was a significant departure from earlier models. It laid the groundwork for modern atomic physics and our understanding of atomic structure and behavior.