in 1911 a British physicist, Ernest Rutherford, proposed a model of the atom with a nucleus exists (a dense central part with a less dense surrounding).

He further postulated that the number of protons in an atom equals the number of the electrons.

He also hypothesized that more neutral particles existed (now known as neutrons) and they help make the nucleus even more dense.

Rutherford created the model to the left after observing how alpha particles (small positive charges) behaved when they were shot at a super thin piece of gold foil (like tin foil, but made of gold).

Why do you think gold was used rather than tin?

The observations that he made were:

  1. MOST of the alpha particles (positive charge) would go straight through the foil
  2. Sometimes, the alpha particles would bend slightly to the side
  3. RARELY, the alpha particle would bounce back off of the foil