Rutherford’s planetary model
Rutherford atomic model says most of the space in the atom is empty (as most of the α – particles passed through the foil undeflected).
A few positive charges were deflected. The deflection must be due to enormous repulsive force showing that the positive charge of the atom is not spread throughout the atom as Thomson predicted. The positive charge is concentrated in a very small volume. Which is responsible for the deflection of α – particles.
On the basis of the above observations, Rutherford proposed the nuclear model. According to his model
- The positive charge in the atom is concentrated in the small dense portion, called the Nucleus.
- The nucleus is surrounded by the electrons that move around it in circular paths called the Orbits. Thus Rutherford’s model resembles the solar system.
- Electrons and the nucleus are held together by electrostatic forces of attraction.
Drawbacks of Rutherford atomic model
- Rutherford’s atomic model of an atom is like a small scale solar system. This similarity suggests that electrons should move around the nucleus in well-defined orbits. However, when a body is moving, it undergoes acceleration. According to electromagnetic theory, charged particles, when accelerated, should emit radiation. Therefore, an electron in an orbit will emit radiation, thus the orbit will continue to shrink. But this does not happen. Thus Rutherford’s model cannot explain the stability of the atom.
- If we assume that electrons as stationary around the nucleus, the electrostatic attraction between the nucleus and the electrons would pull the electrons towards the nucleus to form a miniature version of Thompson’s model.
- Rutherford model does not explain the electronic structure of the atom i.e., how the electrons are distributed around the nucleus and what are the energies of these electrons.
Before studying further developments that lead to the formulation of various atomic models, it is necessary to study about light and its nature.