Atomic Theory Timeline

Democritus

400 BCE

Said everything was composed of atoms. Said atoms can't be split any further. Said atoms are indestructible.

Aristotle

300 BCE

Disagreed with Democritus. Believed there were only four elements: air, earth, fire, and water. Said there were no atoms.

Georg Bauer

1494

Presented the first scientific classification of minerals.

Robert Boyle

1688

Wrote a book that overturned Aristotle's concept of the four elements.

Antoine Lavoisier

1778

Developed Law of Conservation of Mass. Recognized and named Oxygen and Hydrogen. Opposed the Phlogiston Theory.

Joseph Proust

1798

Developed Law of Definite Proportions.

John Dalton

1808

Proposed that elements consisted of atoms that were identical and had the same mass and that compounds were atoms from different elements combined together.

Joseph Gay-Lussac

1808

Developed the Law of Combining Volumes.

Amedeo Avogadro

1811

Developed Avogadro’s law.

J.J. Thomson

1897

J.J. Thomson discovered the first subatomic particle (the electron).

Henri Becquerel

1903

Realized that some invisible radiation had been emitted from the uranium.

Robert Millikan

1910

Discovered that electrons charge is negative. Used the oil drop experiment.

Neils Bohr

1913

Created the Bohr model of the atom.

Ernest Rutherford

1917

Discovered that the nucleus was surrounded by a void before the cloud of electrons.

Max Planck

1918

Originator of the quantum theory of energy.

Louis de Broglie

1924

Discovered the wave nature of electrons and suggested that all matter have wave properties.

Werner Heisenberg

1925

Created the theory of quantum mechanics.

Erwin Schrodinger

1926

Created the quantum mechanical model of the atom.