Atomic Timeline

Events

Democratis

Approx. 400 B.C.

Came up with idea of atom, model had no protons, neutrons, or election. Solid (small pointy atoms), liquid (large round atoms), oils (fine small atoms that could slip past each other).

Aristotle

300 B.C.

Could understand things/figure out things by just looking at them (Earth, fire, water, and wind). All one material, no particles at all.

Antoine Lavoisier

1778

Came up with law of conservation of mass. Hinted at rearrangement of matter during reactions. Named oxygen and hydrogen (1778, 1783)

John Dalton

1803

All matter is made of atoms, all atoms are identical in mass and properties, chemical reaction is a rearrangement of atoms, compounds are formed by combination of 2 or more atoms (even numbered ratios)

JJ Thomson

1897

Discovered electrons. Was first scientist to show that the atom was made of even smaller things.

Robert Millikan

1910

Determined the charge of an electron. Proved Einstein's photoelectric equation.

Ernest Rutherford

1911

Discovered protons and the nucleus. Also showed that atoms are mostly empty space.

Niels Bohr

1913

Improved Rutherford's model. He proposed that electrons move around the nucleus in shells.

Werner Heisenberg

1925

Proposed that electrons absorb and emit radiation of fixed wavelengths when jumping between fixed orbits around a nucleus.

Erwin Shrodinger

1926

Proposed that elections are arranged in concrete circular orbits around the nucleus.

James Chadwick

1932

Discovered the neutron. Said electrons orbited the neutrons and protons.

Murray Gell-mann

1969

Gell-mann proposed that quarks make up protons and neutrons.