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Atomic Theory Timeline

Exemplar

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Democritus

What did he contribute to atomic theory?

  • The “discovery” of the atom. The smallest, indivisible piece of matter was what he called the atom. They were all the same material.

What was the model they developed?

  • The basic atom, a sphere shape. Named atomos, “not to be cut”.

How did he arrive at his conclusions?

  • He wondered if matter could be divided infinitely or if there was a limit. He also found atoms were infinite and could join together and be different sizes.

Atom Model

~460 BC

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John Dalton

What did he contribute to atomic theory?

  • Started atomic theory. He said all matter is made up of atoms, atoms in a mass are identical, a compound is an combination of two or more different atoms, a chemical reaction is a rearrangement of atoms, and atoms cannot be created or destroyed.

What was the model they developed?

  • Billiard ball model, basically the same thing as Democritus.

How did he arrive at his conclusions?

  • Experiments with different chemicals. Also an interest in meteorology.

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Indivisible

Solid

Sphere

Model

~1808

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J.J. Thomson

What did he contribute to atomic theory?

  • Discovered the electron, and knew they had a negative charge. Thought matter must have a positive charge.

What was the model he developed?

  • The plum pudding model, raisins (electrons) stuck on pudding (atom).

How did he arrive at his conclusions?

  • He was interested in atomic structure. Also proved atoms were not indivisible.

Plum

Pudding

~1897

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Robert Millikan

What did he contribute to atomic theory?

  • Proved the charge of electrons with the falling drop method.

What was the model they developed?

  • None known.

How did he arrive at his conclusions?

  • Interested in exploring electricity, optics, and molecular physics. Multiple experiments.

~1910

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Ernest Rutherford

What did he contribute to atomic theory?

  • Described the makeup of the atom. Almost all the mass was concentrated at the center (the nucleus).

What was the model they developed?

  • Planetary model, and alpha rays through an atom.

How did he arrive at his conclusions?

  • Gold Foil experiment. Thought it would be interesting to see what happens to atoms with alpha rays.

1911

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Niels Bohr

What did he contribute to atomic theory?

  • Fixed Rutherford’s model, and said electrons orbit the nucleus and had fixed orbits. He also figured about the energy levels.

What was the model they developed?

  • The orbits of atoms and the electron shells of atoms.

How did he arrive at his conclusions?

  • He studied under JJ Thomson and Ernest Rutherford.

Electron Cloud

Models ~1912

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Louis de Broglie

What did he contribute to atomic theory?

  • He showed what matter waves would behave like if they existed at all.

What was the model they developed?

  • The predicted waves vs. the original orbits.

How did he arrive at his conclusions?

  • He thought about particles of matter. He thought that light can exist as both particles and waves so atom particles could also behave like waves.

~1924

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Werner Heisenberg

What did he contribute to atomic theory?

  • Uncertainty Principle

What was the model they developed?

  • A small wavelength of light has a high energy. An electron will absorb that energy. The absorbed energy will change the electron's position.

How did he arrive at his conclusions?

  • He had a theory called matrix mechanics which explained the behavior of atoms. It was based on matrices that fit with the idea of electrons as particles.

~1925

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Works Cited

"About This Artwork." Democritus, the Laughing Philosopher. Art Institute Chicago, n.d. Web. 31 Mar. 2014. <http://www.artic.edu/aic/collections/artwork/111427>.

Barkanic, S. "Home." The History of the Atom. Tangient LLC, 23 Nov. 2010. Web. 04 Apr. 2014.< http://the-history-of-the-atom.wikispaces.com/>

Berryman, Sylvia. "Democritus." Stanford University. Stanford University, 15 Aug. 2004. Web. 31 Mar. 2014. <http://plato.stanford.edu/entries/democritus/>.

"Ernest Rutherford Biography." Bio.com. A&E Networks Television, n.d. Web. 31 Mar. 2014. <http://www.biography.com/people/ernest-rutherford-39099>.

"From Quanta to Quarks." Senior Physics and Religion. Bob Emery, 10 Jan. 2013. Web. 04 Apr. 2014. http://webs.mn.catholic.edu.au/physics/emery/hsc_quanta_quarks.htm

"John Dalton." Homepage of the Chemical Heritage Foundation. Chemical Heritage Foundation, 2010. Web. 31 Mar. 2014. <http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/the-path-to-the-periodic-table/dalton.aspx>.

"Joseph John Thomson." Homepage of the Chemical Heritage Foundation. Chemical Heritage Foundation, 2010. Web. 31 Mar. 2014. <http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/atomic-and-nuclear-structure/thomson.aspx>.

"Louis De Broglie - Biographical." Nobelprize.org. Nobel Media AB, n.d. Web. 04 Apr. 2014. http://www.nobelprize.org/nobel_prizes/physics/laureates/1929/broglie-bio.html

Mokeur, Professor. "HISTORY OF THE ATOM FROM DEMOCRITUS TO BOHR AND SCHRÖDINGER." HISTORY OF THE ATOM FROM DEMOCRITUS TO BOHR AND SCHRÖDINGER. Dynamicscience.com.au, 2003-2010. Web. 31 Mar. 2014. <http://profmokeur.com/chemistry/history_of_the_atom.htm>.

"Niels Bohr." Niels Bohr. NNDB, n.d. Web. 01 Apr. 2014. <http://www.nndb.com/people/560/000024488/>.

"Robert A. Millikan - Biographical." Nobelprize.org. Nobel Media AB, 2013. Web. 31 Mar. 2014. <http://www.nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.html>.

"Rutherford Model of the Atom." , Gold Foil Experiment. NCS Pearson, n.d. Web. 31 Mar. 2014. <http://chemistry.tutorvista.com/inorganic-chemistry/rutherford-model-of-the-atom.html>.

Walker, Jim. "History of Atoms." No Beliefs. E-Prime, Nov. 2004. Web. 04 Apr. 2014. http://www.nobeliefs.com/atom.htm

"Werner Heisenberg - Biographical." Nobelprize.org. Nobel Media AB, n.d. Web. 03 Apr. 2014. http://www.nobelprize.org/nobel_prizes/physics/laureates/1932/heisenberg-bio.html