Explain Rutherford's argument for scattered $\alpha $ -particles. 

Rutherford argued that since large number of $\alpha$-particles are scattered at very small angles, atoms must be largely hollow.

If a large part of the mass of atom is tightly concentrated at its centre and it has a positive charge, then Coulomb repulsive force may act between this positive charge and positive charges of $\alpha$-particles.

If so, then the incoming $\alpha$-particle could get very close to the positive charge without penetrating it and it will deflected.

This argument supported the hypothesis of the nuclear atom. This is why Rutherford is credited with the discovery of the nucleus.

He argued that the electron is a short distance from the nucleus. As the planets orbit the Sun, the electrons will orbit around the nucleus in a fixed orbit.

Rutherford's experiments suggested the size of the nucleus to be about $10^{-15} \mathrm{~m}$ to $10^{-14} \mathrm{~m}$. From kinetic theory, the size of an atom was known to be $10^{-10} \mathrm{~m}$ about $10,000$ to $1,00,000$ times larger than the size of the nucleus.