What was Ernest Rutherford's main contribution to the atomic model based on his gold foil experiment?

• A. He suggested that atoms are indivisible solid spheres.
• B. He proposed that atoms have a small, dense, positively charged nucleus.
• C. He discovered that electrons are arranged in fixed orbits around the nucleus.
• D. He introduced the concept of electron clouds with uncertain positions.

Answer: (B)

Verified step by step guidance

1. Understand the historical context: Before Rutherford's experiment, the prevailing atomic model was the 'plum pudding model,' which suggested that atoms were diffuse clouds of positive charge with electrons embedded randomly.
2. Recall the gold foil experiment: Rutherford directed alpha particles at a thin sheet of gold foil and observed their scattering patterns using a fluorescent screen.
3. Analyze the observations: Most alpha particles passed straight through the foil, but some were deflected at large angles, and a few even bounced back, which was unexpected under the plum pudding model.
4. Interpret the results: Rutherford concluded that the atom must have a small, dense, positively charged center (nucleus) that repelled the positively charged alpha particles, causing the deflections.
5. Summarize the main contribution: Rutherford proposed the nuclear model of the atom, where electrons orbit a central nucleus, fundamentally changing the understanding of atomic structure.