Atomic theory By wesley bodwell

Democritus 400Bc


Democritus theorized that all matter is made up of small invisible objects that are uncuttable.

His idea of what an atom looked like

Aristotle 300BC

Aristotle believed that all matter was made up of earth, fire wind, and water.

Due to Aristotles status, everyone believed him and his theory instead of Democritus. Even though Democritus was right

John dalton 1803-1808

He believed like Democritus that all matter is made up of indestructible atoms. He also believed that atoms are constantly moving in empty space.

His idea of what an atom looked like

JJ Thomson 1897

He made the discovery of negative particles in an atom. He made the discovery by using cathode ray tubes, and he used positive and negative magnetic plates

Positive and negative particles

He came up with the plum pudding model. He used this model to back his theory.

Ernest Rutherford 1911-1918

Rutherford had his students experiment with Thomsons discovery. They did this by using gold foil and alpha particles. Most of the alpha particles went straight through the foil. They then came to the conclusion that the particles are mostly empty space.

He used the gold foil experiment to back his theory.

Sir James Chadwick

He made an experiment of combining a sample of beryllium and alpha particles. This made the beryllium emit a strange radiation. He then discovered this radiation when it hits paraffin wax it dislodges some protons. He then was convinced the beryllium was emitting neutrons.

He was the first to discover neutrons.

Niels Bohr 1912

His discoveries led to different models for the structure of the atom. Bohr then proposed a theory for the hydrogen atom based on quantum theory. That energy is transferred only in certain well defined quantities. Another idea of his was that electrons move around but only in prescribed orbits. When jumping from one orbit to another with low energy, a light quantum is emitted.

could explain why atoms emit lights in fixed wave lengths.

Erwin shrodinger 1926

Created the wave equation of non relativistic quantum mechanics. He showed that waves can be used to describe electrons in atoms.

His model shows the floating motion of the electrons, rather than having a set path for travel. He also said any electron stuck to an orbit would set up standing waves. His idea was you can only describe where an electron could be.

Louis de broglie 1924

Discovered that electrons have properties of both waves and particles. The wave name was the matter wave.

Werrner Heisenberg 1927

Made the uncertainty principle. Said it's not possible to find the exact position and momentum.

His model determined that the only way to describe an atom is through probability distribution.

Work cited

"James Chadwick - Biography." Web. 19 Nov. 2011. <>

"J.J. Thomson - Biography." Web. 19 Nov. 2011. <>.

"John Dalton | Chemical Heritage Foundation." Homepage of the Chemical Heritage Foundation | Chemical Heritage Foundation. Web. 19 Nov. 2011. <>.

"Werner Heisenberg - Biography." Web. 19 Nov. 2011. <>.

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