Atomic theory timeline By Tahlia Jones

Democritus- The proposal of atoms

460 BCE

Democritus proposed that matter could not be divided into smaller pieces forever. He claimed that matter is made of small hard particles called atoms.

John Dalton- Created the first atomic theory.

1803

John Dalton thought of atoms as being tiny round balls he also created the very first atomic theory.

Henri Becquerel- Discovered radioactivity in some atoms.

1896

Henri Becquerel found out that some atoms have natural radioactivity. His research helped to perfect the later version of the atomic model.

J.J. Thompson- Atoms are made of smaller things

1897

J.J. Thompson created the atomic model known as the raisin bun model. He showed that an atom is made of even smaller things.

Ernest Rutherford- Discovered protons and the nucleus

1907

Ernest Rutherford showed that some atoms have particles in the centre and are mostly empty space. He discovered protons and the nucleus.

Robert Millikan- Determined the charge of an electron

1910

Robert Millikan determined the charge of an electron by using his oil drop experiment. He figured out that one electron carries one unit of negative charge and 1/1840 the mass of a proton.

Niels Bohr - Discovery of electron shells

1913

Niels Bohr created the theory for the hydrogen atom and the theory that electrons move around the atom in specific layers or shells.

James Chadwick- Discovered neutrons

1932

Working with Ernest Rutherford's he discovered particles with no charge therefore calling these particles neutrons.