Write down the observations and conclusions of the $\alpha$-particle scattering experiment.

(N/A) Observations:
$(i)$ Most of the $\alpha$-particles passed through the gold foil undeflected.
$(ii)$ $A$ small fraction of the $\alpha$-particles was deflected by small angles.
$(iii)$ $A$ very few $\alpha$-particles (about $1$ in $20,000$) bounced back,that is,were deflected by nearly $180^{\circ}$.
Conclusions on the basis of the $\alpha$-particle scattering experiment:
$(i)$ Most of the space in the atom is empty as most of the $\alpha$-particles passed through the foil undeflected.
$(ii)$ $A$ few positively charged $\alpha$-particles were deflected. The deflection must be due to an 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 $\alpha$-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 $10^{-10} \ m$,while that of the nucleus is $10^{-15} \ m$. One can appreciate this difference in size by realizing that if a cricket ball represents a nucleus,then the radius of the atom would be about $5 \ km$.