Question

Describe briefly Rutherford's \(\alpha\)-particle scattering experiment. What are the shortcomings of this model? How are they rectified in Bohr's model?

Hint:

Bohr's model introduced quantized orbits to explain atomic stability and the spectral lines of hydrogen, something Rutherford's model could not account for.

Answer 1

Rutherford's \(\alpha\)-Particle Scattering Experiment:
In Rutherford's experiment, a beam of \(\alpha\)-particles was directed at a thin gold foil. By observing the scattering angles of the \(\alpha\)-particles, Rutherford concluded that most of the mass of an atom is concentrated in a tiny, dense nucleus at the centre, and that the majority of the atom's volume is empty space. The \(\alpha\)-particles were deflected at large angles by the positive charge concentrated in the nucleus. This led to the discovery of the nuclear model of the atom, where electrons orbit around a dense nucleus. Shortcomings of Rutherford's Model:
Rutherford's model, while groundbreaking, had certain flaws:
- It did not explain the stability of the atom. According to classical electromagnetism, the revolving electrons would emit radiation, causing them to lose energy and spiral into the nucleus, leading to atomic collapse.
- It could not explain the observed spectral lines of hydrogen, as predicted by experimental data, where the electron should continuously radiate energy and not remain in discrete energy levels.
Rectification by Bohr's Model:
Niels Bohr improved upon Rutherford's model by introducing the idea that electrons exist in discrete orbits or energy levels. The electrons can only occupy these stable orbits without radiating energy. Radiation occurs only when an electron jumps from one orbit to another. The energy associated with these orbits is quantized, and Bohr used this idea to explain the discrete spectral lines observed in hydrogen.