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400 BCE
Democritus
Democritus was the one who gave the atom its name. He belied that the atom was indivisible and unchangeable. He also believed that the atom was homogeneous and atoms differ in size, shape, mass, position and arrangement, with a void exists between them. -
322 BCE
Aristotle (hylomorphism)
Aristotle believed in his theory called hylomorphism. This was thought that atoms were made up of the four elements. Earth, Air, Fire and Water. He believed that there wasn’t separate particles but that it was all one. -
John Dalton (Billiard Ball Model)
He names his theory the Billiard Ball Model. This is the theory that explains each atom is a different element and elements can combine to create a compound. -
Dmitri Mendeleev
Dmitri developed the first periodic table of elements. He organized the table by their atomic mass. This helped with the development with the atom a lot because it gave people an idea of what atoms could be made of or what they were. -
JJ Thomson (plum pudding model)
Just Thomson believed in something called the plum pudding model. This is the theory that means that each atom sphere was filled with positively charged fluid but had small scattered negative charged electrons throughout. -
Ernest Rutherford (Planetary Model)
Ernest Rutherford had a theory that there was a nucleus with positively charged protons and then negatively charged electrons around the nucleus. He figured this out by using the gold foil Experiment. -
Henry Moseley
Henry Mosley added on to the periodic table by explaining that there is a different amount of proton for each element. And that elements were organized wrong he changed the periodic table to where they were in the order of how many protons it had also known as atomic number. -
Niels Bohr (Solar system model)
Bohr’s atom like Rutherford’s contained a dense, positive nucleus. He stated that the electron moved in fixed, circular orbits (or energy levels) around the nucleus, these called electron shells. These shells were at set distances from the nucleus and were the same for all atoms. He stated they became larger the further away they are from the nucleus, and that electrons furthest from the nucleus have higher energy. -
Schrodinger and Heisenberg
Schrodinger and Heisenberg Discovered that electrons do not travel in fixed lines instead they roam in waved and have no fixed or exact location. -
James Chadwick
James Chadwick discovered the neutron. He said that the neutron had no charge or was neutral. He also thought that it was roughly that same mass as the proton. He created a new model that was more accurate and helped chemists understand how atoms work more.
