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Chapter 6: Problem 30

Discuss the way in which Thomson's model is nonphysical. Support your argument with experimental evidence.

Short Answer

Expert verified
In conclusion, Thomson's plum pudding model is nonphysical because it fails to explain the results of the Geiger-Marsden experiment, where alpha particles exhibited large deflections that implied the presence of a concentrated positive charge within the atom, contradicting the diffuse positive charge distribution in the plum pudding model. The more accurate and physical representation of atomic structure is provided by Rutherford's nuclear model, which introduced a dense, positively charged nucleus surrounded by orbiting electrons.

Step by step solution

01

Describe Thomson's Plum Pudding Model

Thomson's model, proposed by J.J. Thomson in 1904, is an early atomic model where atoms are made up of negatively charged electrons distributed throughout a positively charged sphere. This model is often referred to as the "plum pudding model," as it resembles the traditional British dessert with electrons representing plums embedded within the positively charged pudding.
02

Explain the Geiger-Marsden Experiment

The Geiger-Marsden experiment, conducted by Hans Geiger and Ernest Marsden under the supervision of Ernest Rutherford in 1909, was aimed at testing the plum pudding model. In this experiment, alpha particles (positively charged particles) were emitted from a radioactive source and directed towards a thin gold foil. A screen coated with zinc sulfide was placed around the foil to measure the locations of scattered alpha particles. If the plum pudding model was accurate, only minor deflections in the alpha particles' paths would be expected.
03

Discuss the Results of the Geiger-Marsden Experiment

The experimental results showed that, although most of the alpha particles passed through the gold foil with little or no deflection, a small fraction of them were deflected at large angles, some even bounced back towards the source of alpha particles. These surprising results could not be explained using the plum pudding model since the deflections implied the presence of a concentrated positive charge within the atom.
04

Introduce Rutherford's Nuclear Model of the Atom

To explain the unexpected results of the Geiger-Marsden experiment, Ernest Rutherford proposed a new atomic model in 1911, known as the nuclear model of the atom. In this model, the positive charge (and most of the mass) is concentrated in a small central nucleus, while the electrons orbit the nucleus at relatively large distances. The large deflections of some alpha particles can be explained by their interactions with the dense and positively charged nucleus.
05

Conclude the Argument on the Nonphysical Nature of Thomson's Model

In conclusion, Thomson's plum pudding model is considered nonphysical as it fails to explain the experimental results obtained in the Geiger-Marsden experiment. The large deflections of some alpha particles could not be accounted for by the diffuse positive charge distribution in the plum pudding model. Rutherford's nuclear model, which proposed the existence of a dense, positively charged nucleus, provided a more accurate and physical representation of atomic structure based on the experimental evidence.

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