science

Democritus

400 BCE

He theorized that all material bodies comprise indivisibly small “atoms.”

John Dalton

1807

based on the concept that each element consists of its own unique brand of indivisible atom

JJ Thompson

1903

discovery that atoms were made up of smaller components

Ernest Rutherford

1911

Rutherford established that the mass of the atom is concentrated in its nucleus

Niels Bohr

1913

proposed a model of the atom in which the electron was able to occupy only certain orbits around the nucleus

James Chadwick

1932

discovery of the neutron in the atom