Both Rutherford’s and Bohr’s models have electrons orbiting the nucleus. Class 9

Both Rutherford’s and Bohr’s models have electrons orbiting the nucleus. Class 9

Question 1.

Both Rutherford’s and Bohr’s models have electrons orbiting the nucleus. Why did Rutherford’s model fail to explain atomic stability, while Bohr’s model succeeded? Class 9

Answer:

The key difference lies in how each model describes the electron's motion:

Rutherford's model and why it failed:

1. In Rutherford's model, electrons orbit the nucleus freely, similar to planets around the Sun.
2. However, according to the laws of physics (as understood from Chapter 4 - describing circular motion), a particle moving in a circular path is constantly changing direction, which means it is accelerating.
3. A negatively charged particle that is accelerating should continuously emit energy (in the form of radiation).
4. If electrons kept losing energy, they would slow down, spiral inward toward the nucleus, and eventually fall into it.
5. If this happened, atoms would collapse in a very short time and would not exist in a stable form.
6. Rutherford's model had no explanation for why this does not happen. It could not explain atomic stability.

Bohr's model and why it succeeded:

1. Bohr introduced the concept of stationary states (fixed orbits/shells).
2. He proposed that when an electron is in a fixed allowed orbit, its energy remains constant - it does not emit or lose energy while in that orbit.
3. This was a postulate (an assumed rule) that Bohr introduced specifically to address Rutherford's limitation.
4. By placing electrons in fixed energy levels where energy is constant, Bohr's model successfully explained why electrons do not spiral inward and why atoms are stable.
5. Bohr's model could also explain many experimental observations, like the spectrum of hydrogen.