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403 BCE
The First Model of The Atom
Democritus creates the first model of the atom. He thought all atoms were the same in size but had different properties. For example, water atoms were round so they could flow and iron atoms were rigid to stick together. His theory was rejected by most Greek philosophers. -
400 BCE
Atomic Theory Slows
For a long period of time, no significant changes were made to atomic theory. -
John Dalton
John Dalton expanded on the first atomic theory to more modernize it. He believed that every atom was in the shape of a ball and that all atoms of the same element had to be the same mass. -
The "Plum Pudding" Model
J.J. Thompson created the next atomic model with what was called the plum-pudding model. He theorized that atoms were composed of negatively charged electrons floating in a positively charged matter. -
Ernest Rutherford
Rutherford disproved the "plum-pudding" model by shooting particles at a sheet of gold, thinking the particles would go through. However, some of the particles bounced back, leading him to create his model with a central nucleus. -
Niels Bohr
Bohr built upon Rutherford's model by proving, to keep the atomic stable, the electrons must be in set orbits. He also concluded that differnt orbits have different levels of energy. -
Quantum Mechanical Model
The modern atomic theory created by Schrödinger shows electrons as not having a stable orbit, but being in possible locations at any given moment. This is the newest and accepted model.
