Atomic Theory Timeline

The Alchemists

700 BCE

Formed a theory which believed that all metals were formed or compounded of sulfur and mercury.

Democritus

465 BCE

Created a theory which follows these rules:
1) Everything is made up of atoms, and they are physically invisible.
2) There is an empty space that exists between atoms.
3) Atoms cannot be destroyed.
4) Atoms are in perpetual motion and will remain to be so.
5) The number of atoms and their type is infinite, and they differ in shape and size.

Plato

427 BCE

Introduced the atomic theory in which ideal geometric forms serve as atoms.

Robert Boyle

1650

Contributed to a theory which believed that all matter is composed of tiny particles.

John Dalton

1803

Created a theory which contained the following:
1) Matter is made up of small and invisible particles called atoms.
2) Atoms of the same element are identical and have the same mass.
3) Atoms of different elements can vary in size, mass, and chemical behavior.
2) Each chemical is composed of atoms of a single and unique type.
5) Atoms cannot be altered or destroyed by chemical means but can be combined to form more complex structures.

Antoine Lavoisier

1803

Performed experiments which showed that the total mass of products and reactants in a chemical reaction is always the same.

Billiard Ball Model

1803

Created by John Dalton, a concept where an atom is a ball-like structure that cannot be divided any further.

Amedeo Avogadro

1811

Proposed a law that states equal volumes of gases contain equal numbers of molecules and that elemental gases are composed of two atoms.

Dmitri Mendeleev

1869

Known for his discovery of the periodic law, which states that when elements are arranged in order of increasing atomic weight, the resulting table displays a recurring pattern of properties within groups of elements.

Solar System Model

1897

First created by Joseph Larmor, but was claimed to be suggested by Jean Baptiste Perrin in 1911, and also had contributions from Niels Bohr in 1913. (Also known to be similar to the Rutherford Model)

Pierre and Marie Curie

1898

Hypothesized that radioactive particles cause atoms to break down and release radiation.

JJ Thomson

1904

Created the Plum Pudding Model.

Plum Pudding Model

1904

Created by J.J. Thomson, it is a representation of electrons surrounded by a sphere of positive charge, like negative-charged "plums" embedded in a positively-charged "pudding".

Albert Einstein

1905

Proved the existence of atoms.

Ernest Rutherford

1911

Discovered that the atom is mostly empty space surrounding a massive nucleus.

Niels Bohr

1913

His theory is a model of the atom that describes electrons as revolving in discrete orbits around a positively charged nucleus.

Robert Millikan

1913

Main contribution was deducing the electric charge of an electron.

Henry G. J. Mosely

1913

Demonstrated that the major properties of an element are determined by the atomic number not by the atomic weight.

Electron Cloud Model

1926

Created by Erwin Schrodinger, which shows that an atom consists of a small but massive nucleus which is surrounded by a cloud of rapidly moving electrons.

James Chadwich

1932

Known for his discovery of the neutron, which states that the nucleus of an atom contains both positively charged protons and neutral neutrons, which have the same mass.