Definition Of Rutherford?s Model Of Atom
The Rutherford model is a model of the atom devised by Ernest Rutherford. Rutherford directed the famous Geiger-Marsden experiment and analysed and suggested the presence of nucleus in an atom
More About Rutherford’s model of atom
- In this experiment, fast moving alpha (α)-particles were made to fall on a thin foil
- Rutherford selected gold foil because he wanted a very thin foil. The gold foil that he selected was as thick as 1000 atoms
- α particles are doubly charged helium ions. They have a considerable amount of energy as their mass is equal to 4u
- It was expected that α-particles would be deflected by the sub-atomic particles in the gold atoms. Since the α-particles were much heavier than the protons, he did not expect to see large deflections
- But most of the α particles passed straight through the gold foil
- Some of the α particles were deflected by a small angle
- One out of 12000 α particles rebounded
- Rutherford concluded that most of the space inside the atom is empty because most of the α particles passed straight through the gold foil
- Very few α particles were deflected by a small angle; hence a small portion of the atom consists of a positive charge
- Few α particles rebounded, therefore, most of the mass and entire positive charge of the atom is concentrated at the centre of the atom called nucleus
- A very small fraction of α particles were rebounded, so the mass and all the positive charge of the atom is concentrated at a very small portion of the atom
- The radius of the nucleus is about times less than that of the atom
- The conclusions of Rutherford are
- There is a positively charged centre in the atom called “nucleus”. Nearly all the mass of the atom is concentrated at the nucleus
- The electrons revolve around the nucleus in well defined orbits
- The size of the nucleus is very small compared to the size of the atom
Applications
- Results can best explained by a model for the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun
- The Rutherford atomic model has been alternatively called the nuclear atom, or the planetary model of the atom
- The electrostatic force of attraction between electrons and nucleus was likened to the gravitational force of attraction between the revolving planets and the Sun
