were deflected by nearly ° . On the basis of the observations, Rutherford drew the following conclusions regarding the structure of atom: (i) Most of the space in the atom is empty as most of the α –particles passed through the foil undeflected. (ii) A few positively charged α –particles 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 had presumed.
The positive charge has to be concentrated in a very small volume that repelled and deflected the positively charged α –particles. (iii) Calculations by Rutherford showed that the volume occupied by the nucleus is negligibly small as compared to the total volume of the atom. The radius of the atom is about – m, while that of nucleus is – m. One can appreciate this difference in size by realising that if Fig.
. Schematic view of Rutherford’s scattering experiment. When a beam of alpha () particles is “shot” at a thin gold foil, most of them pass through without much effect. Some, however, are deflected.
A. Rutherford’s scattering experiment B. Schematic molecular view of the gold foil . .
Rutherford’s Nuclear Model of Atom Rutherford and his students (Hans Geiger and Ernest Marsden) bombarded very thin gold foil with α –particles. Rutherford’s famous –particle scattering experiment is particles similar to electrons. The γ -rays are high energy radiations like X-rays, are neutral in nature and do not consist of particles. As regards penetrating power, α -particles are the least, followed by β -rays ( times that of α –particles) and γ -rays ( times of that α -particles).
a cricket ball represents a nucleus, then the radius of atom would be about km. On the basis of above observations and conclusions, Rutherford proposed the nuclear model of atom. According to this model: (i) The positive charge and most of the mass of the atom was densely concentrated in extremely small region. This very small portion of the atom was called nucleus by Rutherford.
(ii) The nucleus