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Period: 100 to Dec 31, 1400
Alchemists
Alchemists continued to work on atomic theories after aristotle, up until circa the 1400s. One of their goals was to find a way to turn ordinary metals into gold. Through experimenting with this, they discovered many things that, today, we call chemical properties. -
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Democritus
Democritus was the first to suggest the existence of atoms. He called these particles "atomos". -
Benjamin Franklin
In 1752, Franklin performed his famous kite experiment. This led him to realize that all matter has charges, which he represented by + and -. -
Antoine Lavoisier
In 1774, Lavoisier proposed the Law of Conservataion of Mass. This law states that atoms can be neither created nor destroyed, and that the mass of the products of a reaction must equal the mass of the reactants. -
Joseph Proust
In 1799, Proust proposed the Law of Constant Composition. This law states that all of the same molecules will be made up of the same elements in the same proportions, regardless of their origin. -
John Dalton
In 1803, Dalton proposed the first atomic theory. He combined the theories of previous physicists to create his final product. -
John Dalton
Dalton proposed the Law of Multiple Proportions in 1803. This law states that two molecules made of the same elements are not the same if the proportions of the elements are different. -
William Crookes
In 1832, Crookes accomplished three main things. He created the first cathode ray tube, he discovered the electron, and he discovered the element thalium. -
Michael Faraday
In 1833, Faraday discovered that molecules coul be split wth electricity. He called this electrolysis. -
Dmitri Mendeleev
In1869, Mendeleev created the first periodic table. He arranged the elements in order of increasing atomic weight and included holes for undiscovered elements. -
Henri Becquerel
Henry Becquerel experimented with unranium in 1896. While doing this, he dicovered radioactivity when a piece of undeveloped photgraph paper became developed when exposed to the uranium. -
Marie and Pierre Curie
In 1896, The Curies worked in collaboration with Henri Becquerel. Together, they discovered radioactivity. They also went on to discover the elements radium and polonium. -
JJ Thomson
In 1897, Thomson discovered the existence of negatively charged particles called electrons. He did this through experimentation with a cathode ray tube. -
Max Planck
In 1900, Max Planck created the Quantum Theory of Energy. Many physicists after him built off of this theory. -
JJ Thomson
In 1904, JJ Thomson proposed the "Plum Pudding" model of the atom. -
Albert Einstein
Einstein accomplished three main things in 1905. He published hi famous equation, E=mc2, he proved the existence of the atom, and proposed the theory that light was made of particles instead of waves. -
Robert Millikan
In 1909, Milllikan performed his oil drop experiment. Through this, he was able to determine the unit charge of an electron, which is 1.60x10^-19 coulombs. -
Ernest Rutherford
In 1911, Rutherfors performed his gold foil experiement. From this, he proped the nuclear atomic model. -
Niels Bohr
Bohr proposed the planetary model of the atom. This model is also known as the Bohr model. -
Ernest Rutherford
In 1920, Rutherford proposed the existence of a third subatomic particle. He said that this particle was neutrally charged and called in a neutron. -
Louis de Broglie
De Broglie said in 1924 that electrons could act as both waves and particles. He also compared them to light. -
Erwin Schrodinger
In 1926, Schrodinger created his Quantum Mechanical Model. He used this model to predict the probability of an electron to be in a certain location. -
Werner Heisenberg
In 1927, Heisenberg realized that we can never know a specific electrons speed and location at the same time. He called this the uncertainty principle. -
James Chadwick
Chadwick discovered the neutron in 1932. This led to the discovery of fission and the atomis bomb. -
Aristotle
Aristotle theorized that all matter on Earth is made up of earth, air, water, and fire. He said that any substance can only be two adjacent properties on his model.
