Chapter 28, Problem 23A

To determine

To Review: The planetary model of the atom.

Explanation of Solution

Introduction:

The model of the atom proposed by Ernest Rutherford is called a 'planetary model' as the electrons revolves around the nucleus similar to the planets which revolves around the sun (The planets are held near the sun by gravity and the electrons are held near the nucleus by the Coulomb force).

The planetary model of the atom has two very important flaws, which are as follows,

1. The planetary model of the atom could not explain the reason that individual atoms have discrete line spectra. On the other hand, as per Rutherford's model, each atom produces a continuous line spectrum.
2. Planetary model is based on the consideration that electrons revolve around the atom in circular orbit. If it was true, the electrons would have accelerated towards the nucleus, radiating energy in the form of electromagnetic waves (according to the Maxwell's theory) which would have implied that the electron would have lost energy according to the law of conservation of energy. Hence, as the electron orbits, it gradually loses its kinetic energy which causes decrease in velocity and making it to spiral and then smash into the nucleus. This would show that atoms are naturally unstable. As atoms are generally stable, it signifies that the planetary model of the atom does not accurately describes the structure of the atom.