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Scientist Project

By Katelyn Hudack

Atomic Theory Timeline

Atomic History Timeline

Democritus - 400 B.C.

Democritus

400 B.C.

Democritus was a Greek Philosopher, who was one of the first atomic theorists. He theorized that all surrounding matter is made up of tiny, indivisible particles, which he called "atomos." Democritus believed that atoms had different shapes and sizes, were in constant motion, collided with one another, and either bounced off or stuck to each other.

Aristotle - 300 B.C.

Aristotle

300 B.C.

Aristotle was an Ancient Greek Philosopher, who did not believe in the atomic theory. Instead, he believed that matter was not made of atoms, but four elements, fire, air, water, and earth. At the time, he had a great influence on the public and his ideas were accepted. This resulted in Democritus' to be dismissed for around 2,000 years. Eventually, Aristotle's view was disproven and no longer present in the modern view of the atom.

Lavoisier - 1778

Lavoisier

1778

Lavoisier insisted that chemistry was not based on speculation, but rather experiments and observation. In one his experiments, he showed the formation of water by combining hydrogen and oxygen in a sealed container. This experiment showed that water is a compound, opposed to an element, as previously believed.

John Dalton - 1803

John Dalton

1803

John Dalton was an English school teacher, who proposed his theory that contained three basic ideas. Tiny particles, called atoms, make up elements. While atoms of one element are identical, different elements had atoms that differed in size and mass. Lastly, atoms join together to form compounds. His model was known as the Billiard Ball Model.

Billiard Ball Model

Billiard Ball

Model

Dalton called his model the Billiard Ball Model because he envisioned atoms as hard, solid spheres, like wooden balls. He added holes in the balls of his model so he could model compounds by joining the spheres together with hooks.

J.J. Thomson - 1896

J.J. Thomson

1897

J.J. Thomson was an English Physicist, who discovered that atoms have electrons, negatively charged particles, using a cathode ray tube. He also discovered an electrons charge to mass ratio. The model he created was the Plum Pudding Model, where electrons are dispersed in a orderly positive charge.

Plum Pudding Model

Thomson's model was an atom that has positively charged space, with negatively charged electrons inside the space. It was called the "Plum Pudding Model" because the positive space was like the pudding and the electrons were like the plums inside.

Robert Millikan - 1909

Robert Millikan

1908

Robert Millikan was an American Physicist at the University of Chicago. His experiment using oil droplets to measure the charge of an electron contributed to the understanding of atom structure and atom theory.

Niels Bohr - 1911

Niels Bohr

1913

Neils Bohr was a Danish Physicist, whose model was based on the hydrogen atom. In Bohr's Orbit Model, the electrons orbit the nucleus. When emitting or absorbing energy, electrons can jump from one orbit to another.

Bohr's Orbit Model

In Bohr's Orbit Model, electrons travel in circular orbits around the nucleus. Similar to the structure of the solar system, it is a system of a small dense nucleus being orbited by electrons.

Heisenberg, Louis DeBroglie and Schrodinger - 1924

Heisenberg, DeBroglie, Schrodinger

1924

Louis DeBroglie was a French graduate student who worked with Schrodinger and Heisenberg. They believed that, similar to light, electrons can behave like waves and particles. Their Wave Mechanical Model is a theory of the location of electrons around the nucleus.

Wave Mechanical Model

Heisenberg, Louis DeBroglie and Schrodinger's Wave Mechanical Model theorizes that electrons are in orbitals, which are not at all like orbits. Orbitals are zones of probability. Their model was supported by experiments carried out by two scientists, Clinton Davisson and Lester Germer.

Citations

American Board for Certification of Teacher Excellence. (2007). Development of the Atomic Theory. Retrieved September 27, 2020, from http://www.abcte.org/files/previews/chemistry/s1_p1.html

Brainard, J. (2020, May 18). Dalton's Atomic Theory. Retrieved September 27, 2020, from https://www.ck12.org/chemistry/daltons-atomic-theory/lesson/Daltons-Atomic-Theory-MS-PS/

Famous Scientists. (2020). Home. Retrieved September 27, 2020, from https://www.famousscientists.org/top-chemists/

Penn Arts & Sciences. (n.d.). Atomic Timeline. Retrieved September 27, 2020, from https://www.sas.upenn.edu/

Science History Institute. (2020, September 22). Michael Faraday. Retrieved September 27, 2020, from https://www.sciencehistory.org/historical-profile/michael-faraday

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