Atomic Theory Timeline by Oriana Rodriguez

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Democritus

492 BCE

He stated that all objects are made up of little indestructible and indivisible things called atoms.

Indivisible, Solid Sphere Model

492 BCE

Aristotle

332 BCE

Aristotle said that all things are made up of form and matter which can only be changed with growth, decay, or motion, and also they are made up of the four main elements, water, earth, air, fire.

John Dalton's atom theory

1803

Dalton created a scientific theory based off of and including Democritus' atom idea: All elements are created from indestructible particles called atoms. His theory was that when atoms of different elements are joined, separated, or rearranged chemical reactions result.

J.J Thompson's studies

1897

When high energy was moved from the negative cathode plate through a vacuum sealed container to a positive plate, it created a beam of electrons. This resulted in the Thompson/Plum Pudding atomic model.

Plum (raisin) Pudding model

1897

Rutherford's discovery

1898

While conducting his gold foil alpha particle scattering experiment, Rutherford observed a flash of light on different places of the phosphorus screen because instead of the alpha particles going straight through the foil with little to no deflections, the beam deflected in multiple directions leading him to determine that atoms had a nucleus.

Max Planck

1900

Radiation experimentation with black body (object that absorbs all electromagnetic radiation) led to his creation of the Planck Postulate that described the stability of electrons.

Robert Millikan

1910

By using the very famous Oil Drop Experiment, Millikan found the charge of an electron to be negative. It's approximately described as 1/1840 the mass of a Hydrogen atom.

Niels Bohr

1913

Using Planck's Quantum Theory and Rutherford's study of the nucleus in atoms, Bohr came to the conclusion that atoms have a heavily charged nucleus with the electrons.

Planetary Atom Model

1913

Louis de Brogile

1923

A French physicist, Louis studied the stability of the atom. He determined that all forms of energy exist in both particles and wavelengths, establishing the wave-particle duality of nature.

Werner Heisenberg

1926

He realized that there are many things about atoms which cannot be exactly determined or calculated. Mainly determining an electrons location and velocity at the same time. This is called the Uncertainty Principle.

Erwin Schrödinger

1926

Based off of Louis de Brogile's work, he came up with the quantum mechanical atomic model which shows the orbitals around the nucleus in constant motion.

Quantum Mechanical Model

1930

James Chadwick

1932

He discovered the existence of neutrons and that they had no charge at all. This allowed for atomic bombs to be made because of the presence of neutrons.