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Period: 500 BCE to
History of the atom model
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400 BCE
Democritus
In 400 B.C., Ancient Greece, Democritus theorized that all the matter in the universe is composed of invisible particles. -
400 BCE
Democritus's atom model
His model was a plain sphere -
John Dalton's atom model
Just like Democritus' model from 400 B.C., Dalton's model was just a plain sphere -
John Dalton
In the early 19th century, John Dalton stated that:
1. All matter is made of atoms. Atoms are invisible and indestructible.
2. All atoms of a given substance are identical in mass and properties.
Dalton may have made this theory while researching ethylene and methane gas, or while researching nitrous oxide and nitrogen dioxide. -
J.J. Thompson
While experimenting with cathode rays, J.J. Thompson discovered that the particles emitted from the cathode ray tube were negatively charged as well as being at least 1000 times lighter than the mass of a hydrogen atom. -
Cathode ray tube
This is a cathode ray similar to the one J.J. Thompson used during his experiments with cathode rays. -
J.J. Thompson's atom model
This model included the Electrons that Thompson had discovered. The Electrons were located in a "soup" of positive charge. -
Ernest Rutherford's gold foil experiment
His experiment setup was close if not exactly how it would have looked. -
Ernest Rutherford
In 1911, Ernest Rutherford shot a beam of alpha particles at a sheet of gold foil, expecting the alpha particles to go straight through the sheet, which would support Thompson's atomic theory. But some of the alpha particles seemed to bounce off of the gold foil. Rutherford then concluded that the atoms had a dense nucleus that the alpha particles were deflected off. -
Ernest Rutherford's atom model
This model included electrons which J.J. Thompson had discovered, but included a dense positively charged nucleus. -
Niels Bohr
Niels Bohr was a danish physicist who proposed that electrons travel on different orbitals depending on how energized they are. -
Bohr's model
This model shows the different energy levels the electron travels on. If the electron is on the first ring, then it would have low energy. If it were on the outer ring, it would have a higher energy level. When the electron moves down a level it will emit a photon, when it moves up a level then it would have absorbed a photon. -
Erwin Schrödinger
Erwin Schrödinger was an Austrian physicist who contributed to quantum theory by creating the quantum mechanical model. -
Erwin Schrödinger’s quantum mechanical model.
Schrödinger’s model was a depiction of his mathematical equations which calculated the chance of an electron being in a certain area around the nucleus. The model does not show how an electron would travel around the nucleus.
