Question

What are the demerits of Rutherford model of an atom ?

Hint:

The failures of Rutherford's model were critical in the development of modern atomic theory. These demerits were later addressed by Niels Bohr, who incorporated the concept of quantization of energy levels for electrons, leading to the Bohr model of the atom.

Answer 1

Step 1: Understanding the Concept:
Rutherford's nuclear model of the atom, proposed after the gold foil experiment, successfully described the atom as having a small, dense, positively charged nucleus with negatively charged electrons orbiting it. However, this model had significant shortcomings when analyzed with the principles of classical physics.
Step 2: Detailed Explanation of Demerits:
The two main demerits (drawbacks) of the Rutherford model are as follows:
1. Instability of the Atom:
According to Maxwell's theory of classical electromagnetism, any charged particle undergoing acceleration must radiate energy continuously in the form of electromagnetic waves.
In Rutherford's model, the electrons are revolving around the nucleus. This circular motion is an accelerated motion.
Therefore, an orbiting electron should continuously lose energy by radiation.
This loss of energy would cause its orbit to shrink, and the electron would spiral into the nucleus in a very short time (calculated to be about \(10^{-8}\) seconds).
This would make the atom highly unstable. However, we know that atoms are stable. Rutherford's model could not explain this stability.
2. Inability to Explain the Line Spectrum:
As the electron spirals inwards towards the nucleus, its speed and frequency of revolution would increase continuously.
According to classical physics, the frequency of the emitted electromagnetic radiation should be equal to the frequency of revolution.
Since the electron's frequency is changing continuously, it should emit a continuous spectrum of radiation.
However, experimental observations show that atoms, like hydrogen, emit a discrete line spectrum, i.e., radiation of only specific frequencies or wavelengths.
Rutherford's model failed to explain the origin of these discrete spectral lines.