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400 BCE
Democritus
Democritus was the first to discover that all matter is made up of atoms. His model of an atom was just a round ball. All Democritus knew was that that atoms were indestructible. -
Period: 400 BCE to
History of the Atomic Model
A timeline depicting the history of the atomic model and its contributors to atomic theory. -
350 BCE
Aristotle
Aristotle didn't believe that atoms existed. He believed that things were made up of elements such as wind, fire, water, and earth. He didn't create an atomic model because he didn't believe in atomic theory. -
Antoine Lavoisier
Antoine Lavoisier founded many elements including things like oxygen and hydrogen. He also created the first table of elements and the first chemistry textbooks. -
John Dalton
John Dalton believed in Democritus' ideas about atomic theory and agreed that atoms were indestructible and made up all matter. He also said that different kinds of atoms combined to create chemical compounds. -
Amedeo Avogadro
Amedeo Avogadro came up with the idea that if gasses had the same volume, pressure, and tempereature, they contained the same amount of molecules. This helped advance atomic theory. -
Jons Jakob Berzelius
Jons Jakob Berzelius created a table of all of the known elements relative atomic weights at the time. This supported Dalton's theory that compounds were made out of combinations of atoms of certain elements. -
Dmitri Mendeleev
Dmitri Mendeleev created the periodic table of elements. This table of elements arranged elements based on their chemical properties and they were put in order of relative atomic mass. -
Henri Becquerel / Discovery of Radioactivity
Henri Becquerel discovered that some elements and atoms were radioactive.This was the first ever discovery of radioactivity. This discovery really began to help to develop the atomic model. -
JJ Thompson / Discovery of the Electron
Thompson was the first person to discover that there were electrons in an atom. He created a model that reflected this discovery which he called the plum pudding model (It has a kind of interesting name). -
Marie Curie
Marie Curie was a famous scientist who discovered many things about the mysteries of radioactivity. Her developments in radioactivity won her a Nobel peace prize and greatly helped increase progress in atomic theory. -
Max Planck
Max Planck came up with the Quantum Theory. He discovered that energy was given off in little packets of energy. This discovery about energy levels in atoms helped further the development of the atomic model -
Robert Milikan
Robert Millikan helped prove JJ Thomson's theory that the electron was 1000 times smaller than the atom with an oil drop experiment. Millikan helped inspire many other scientists to pursue development of the atomic model. -
Ernest Rutherford's Nuclear Model / Discovery of the Proton
Ernest Rutherford changed the atomic model. He believed that Thomson's model was incorrect and that the positive force was just located in the center of the atom at a nucleus in the form of a proton. This was the first discovery / acknowledgement of the proton. He also claimed that the atom was filled with mostly empty space. -
Niels Bohr
Niels Bohr was a student of Rutherford's that developed a new model based on Rutherford's. His model created orbits for electrons in an atom and also created levels of energy where only a certain number of electrons could be located. This model is very famous and still used today. -
Henry Moseley
Henry Moseley worked with Bohr to discover the real atomic number of an element on the periodic table. He used x-rays to discover that the amount of neutrons and protons in an atom related to the atomic number of an element of that atom. -
Erwin Schrodinger's Quantum Mechanical Model
Erwin Schrodinger worked on the quantum model of an atom.He disagreed with Bohr's model and theory so he created his own. He believed that the only way to find where an electron was located and how much energy it had was to calculate its probability of being a certain distance away from an atom. -
Werner Heisenberg
Werner Heisenberg proposed that it is impossible to determine the exact velocity and momentum of an electron at the same time. This helps prove some error in Bohr's model due to the fact that the location of the electron in Bohr's model is unknown. -
James Chadwick / Discovery of the Neutron
James Chadwick made an extremely important discovery. He discovered the neutron. He found this out because there was a difference in the number of protons and the atomic mass of an atom. This led to his important discovery of the neutron. -
Lise Meitner
Lise Meitner was the first person to discover nuclear fission. She was a brilliant scientist and discovered that the uranium atoms could split through a process called fission. This process releases great amounts of energy and the discovery of this led to one of the greatest weapon races in history. The race for the nuclear bomb.
