On bombarding a beam of $\mathrm{\alpha }$-particles on the atom of the gold sheet, a few particles get deflected whereas most of them go straight and remains undeflected. This is due to

the neutrons in the nucleus do not have any effect on $\mathrm{\alpha }$-particles 

the force of repulsion on fast moving $\mathrm{\alpha }$-particles is very small

the force of attraction on $\mathrm{\alpha }$-particles by the oppositely charged electron is not sufficient

$\text{ the nucleus occupies much smaller volume as compared to the}$$\text{volume of atom}$