Atomic Model Timeline

By Caroline Burkemper

Atom Model Timeline

By Caroline Burkemper

Democritus of Adbera

460 BC - 370 BC

(1) Matter consists of separate, partless, solid, eternal, immutable, invisible and intangible unit-particles which are physically and theoretically indivisible atoms (the ‘uncuttable’);
(2) Atoms differ in shape (A from B), position (Z from N) and order (AN from NA) but not in quality;
(3) Empty space or void is necessary for their movement;
(4) Perceptible change and plurality are the result of the transfer of momentum by the moving atoms and such transfer occurs only by contact and not by distinct action.
(solid sphere model)

Aristotle

384 BC - 322 BC

Aristotle believed in the 5 elements of fire, air, earth, water, and aether.

John Dalton

1766 - 1844

1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms.

Joseph John Thomson

1856 - 1940

JJ Thomson discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge-to-mass ratio.
(plum pudding model)

Max Planck

1858 - 1947

Planck discovered that each quantum's energy is equal to the frequency of radiation multiplied by the universal constant.
(quantum mechanical model)

Robert Millikan

1868 - 1953

He found that electrical charges, more specifically, electrical charges carried by electrons. His discovery was accomplished by spraying minute drops of oil into a specially built chamber.

Ernest Rutherford

1871 - 1937

Rutherford's atomic theory describs the atom as having a central positive nucleus surrounded by negative orbiting electrons. The Gold Foil Model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space.
(planetary model)

Neils Bohr

1885 - 1962

Neils believed that electrons travel in stationary orbits defined by their angular momentum.

Erwin Schrödinger

1887 - 1961

Erwin took the Bohr atom model one step further. He used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom.

James Chadwick

1891 - 1974

James Chadwick proved the existence of neutrons. As uncharged particles in atoms, neutrons play a key part in nuclear fission, or the splitting of atoms.

Louis de Broglie

1892 - 1987

His ideas were a basis for developing the wave mechanics theory. This theory has greatly improved our knowledge of the physical nature on the atomic scale.

Werner Heisenberg

1901 - 1976

Werner calculated the behavior of electrons, and subatomic particles that also make up an atom. Instead of focusing mainly on scientific terms, this idea brought mathematics more into understanding the patterns of an atom's electrons.