Atomic Model Timeline

Aristotle

400

What: He developed a theory that was based on the four elements. How: Aristotle’s theory made a great generalization of all matter of the four elements: fire, water, earth, and air. He also believed that there were four qualities to these elements: dryness, hotness, coldness, and moistness.

Democritus

460

What: He created the first atomic model. How: His model of the atom depended on analogies from human senses.

John Dalton

Oct 30, 1803

What: Proposed his modern theory of the atom. How: He based it upon :
1. Matter is made up of atoms that are indivisible and indestructible.
2. All atoms of an element are identical.
3. Atoms of different elements have different weights and different chemical properties.
4. Atoms of different elements combine in simple whole numbers to form compounds.
5. Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged.

William Conrad Roentgen

Oct 28, 1895

What: Discovered x-rays while using cathode-ray tubes. How: Found that x-rays could pass
through solid objects.

J.J. Thomson

Oct 29, 1897

What: He discovered the Plum Pudding Model of the atom. How: In J.J.'s model, the atom is composed of electrons surrounded by an area of positive charges to balance out the negative charges.

Hantaro Nagaoka

Oct 29, 1904

What: Nagaoka developed an early, incorrect "planetary model" of the atom. How: The model was based on the stability of Saturn's rings.

Ernest Marsden

Nov 1, 1909

What: He discovered the existence of the atomic nucleus. How: He discovered this by using the Gold Foil Experiment or the Rutherford Experiment.

Ernest Rutherford

Oct 31, 1911

What: Theorized that atoms have their positive charge concentrated in a very small nucleus. How: He pioneered the Rutherford model of the atom, with his discovery and interpretation of Rutherford scattering in his gold foil experiment.

Niels Bohr

Oct 31, 1913

What: Presented a picture of an atomic structure. How: He passed on to a study of the structure of atoms based on Rutherford's discovery of the atomic nucleus. (This lead him to the picture of his atom.)

Henry Moseley

Nov 1, 1913

What: Moseley's law advanced atomic physics
How: He did this by providing the first experimental evidence of Niels Bohr's theory.

Louis de Brogile

Oct 31, 1924

What: He developed a theisis of important findings. How: It served as the basis for developing the general theory now known by the name of wave mechanics, a theory which has utterly transformed our knowledge of physical phenomena on the atomic scale.

Erwin Schrödinger

Oct 31, 1926

What: He generated a mathematical model for the distribution of electrons in an atom. How: He combined the equations for the behavior of waves with the Louis de Broglie equation.

James Chadwick

Oct 31, 1932

What: He proved the existence of neutrons. How: He heard of a new method of detecting particles emitted by radioactive elements developed by Irene Joliot-Curie.