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465 BCE
Democritus' Model of the Atom
Democritus' atom model was just a simple sphere. -
465 BCE
Democritus
Democritus theorizes that everything is composed of smaller versions of itself called atoms. He does not conduct any experiments. -
John Dalton
John Dalton conducts gas experiments, and creates his atomic theory, stating that all atoms of an element are identical, that atoms of different elements differ in size and mass, that atoms cannot be created or destroyed, and compounds can only be created in set ratios of the respective atoms. -
John Dalton's Model of the Atom
John Dalton's atom model was also a simple sphere. -
JJ Thomson
Through his experiments with the Crooke's Tube, Thomson found that the cathode rays could be deflected by electric and magnetic fields. He concluded that instead of being made of light, these rays were composed of negatively charged particles he called corpuscles (later called electrons). -
Crooke's Tube
Used by JJ Thomson, this device consists of a sealed glass container with two electrodes separated by a vacuum. When voltage is given to the electrodes, cathode rays are formed. -
JJ Thomson's Model of the Atom (Plum Pudding Model)
Thomson's atom model shows a positive sphere (‘pudding’) encompassing the entire atom, with negative electrons (‘plums’) scattered throughout the atom. -
Ernest Rutherford
In his gold foil experiment, Rutherford found that most ɑ particles traveled straight through the foil, but some deviated in various directions, including right back to the source. This led him to believe that at the center of the cell, there must be a positively charged mass. -
Gold Foil Experiment
Rutherford’s experiment utilized a radioactive source to shoot ɑ particles towards a piece of gold foil. Surrounding the foil was a 360° phosphorescent screen to detect where the ɑ landed. -
Rutherford's Model of the Atom
Rutherford's atom model was the first to contain a nucleus, a mass of positively charged particles at the center of the atom. -
Neils Bohr's Model of the Atom
Because Ernest Rutherford's model of the atom could not explain the different chemical properties of different elements, Neils Bohr created his model of the atom, which shows a positively charged nucleus (without individual particles composing it), orbited by electrons in numerous energy levels. These energy levels get closer to each other the farther away from the nucleus that they get. -
Erwin Schrödinger’s Model of the Atom
Following Bohr's model of the atom, which could not explain the behavior of elements with more than 1 electron, Erwin Schrödinger created his quantum mechanical model of the atom which shows a positively charged nucleus orbited by electrons, but his model shows a cloud of electrons that represent the possible locations of them, rather than fixed orbits. The more dense an area is, the more likely an electron is to be there, still showing energy levels.
