Ernest Rutherford was a New Zealand Physicist working in England. In 1910, he carried out a simple but clever experiment, from which he showed that an atom has a nucleus.
Rutherford used small positively charged particles (called alpha particles) to bombard a very thin of gold foil. When hit the fluorescent, a small flash of light was produced, seen through a microscope. He found the alpha particles went straight through the gold foil.
some of the alpha particles deflected slightly and a few alpha particles bounced straight back.
Therefore, atom must be mostly empty space, there is a small dense object at the centre of the atom and has negatively charged particles ( electron)