Problem 13 - Chemistry: An Atoms-Focused Approach

Question

Explain how the results of the gold-foil experiment led Rutherford to dismiss the plum-pudding model of the atom and create his own model based on a nucleus surrounded by electrons.

Step-by-Step Solution

Answer

Answer: The gold-foil experiment revealed that the atom had a small, positively charged nucleus at its center, surrounded by orbiting electrons. This suggested that most of the atom was empty space, contrary to the plum-pudding model which proposed a diffuse, positively charged "pudding" with electrons scattered throughout.

Step 1: Understand the plum-pudding model of the atom

The plum-pudding model, proposed by J.J. Thomson, suggested that an atom was composed of a diffuse, positively charged "pudding" with negatively charged electrons scattered throughout. This model was proposed based on the discovery of the electron, which suggested that atoms must have negatively charged particles to balance the positive charges.

Step 2: Explain the gold-foil experiment

Ernest Rutherford conducted the gold-foil experiment to test the plum-pudding model. He directed a stream of alpha particles (positively charged particles) at a thin foil of gold, expecting the alpha particles to be either deflected or absorbed. The experiment used a detecting screen coated with zinc sulfide to observe any deflections or reflections.

Step 3: Describe the unexpected observations

In the gold-foil experiment, most of the alpha particles passed straight through the gold foil, without any noticeable deflection. However, a small number of alpha particles were deflected at large angles, and some even rebounded back towards their source.

Step 4: Dismiss the plum-pudding model

The fact that most alpha particles passed straight through the gold foil without being deflected suggested that the majority of the atom was actually empty space, contrary to the plum-pudding model. The significant deflection of some alpha particles and the rebounding of others indicated the presence of a concentrated, positively charged area in the atom, which caused these particles to be repelled or deflected.

Step 5: Create Rutherford's nuclear model of the atom

Based on the results of the gold-foil experiment, Rutherford proposed a new model of the atom called the nuclear model. In this model, the atom was mostly empty space, with a small, positively charged nucleus at its center. The negatively charged electrons were proposed to orbit the nucleus, separated by a large distance relative to their size.

Step 6: Summarize the significance of the gold-foil experiment

The gold-foil experiment, conducted by Ernest Rutherford, was crucial in disproving the plum-pudding model of the atom and leading to the development of the nuclear model. This experiment demonstrated that atoms were not diffuse, positively charged "puddings" with electrons scattered throughout, but rather had a central nucleus surrounded by orbiting electrons.