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442 BCE
Democritus
Democritus is an ancient Greek philosopher who first used the word “Atom”. Democritus created the theory of the atom and he concluded that all mater is made up of the invisible particles called atoms. -
399 BCE
Plato
Plato introduced the atomic theory in which ideal geometric forms serve as atoms, according to which atoms broke down mathematically into triangles, such that the form elements had the following shape: fire (tetrahedron), air (octahedron), water (icosahedron), earth (cube). -
332 BCE
Aristole
History of the Atomic Theory. Timeline created by jpopgirl12. In Science and Technology. 200. 332 BCE - Aristotle's Discovery. Although the date is approximate, Aristotle concluded in his Metaphysics book that all things are made up of form and matter which can only be changed with growth, decay, or motion. -
Robert Boyle
“The Father of Chemistry” for his discovery that atoms must exist based on the relationship between pressure and volume of gas. His theorem called Boyle’s Law reasons that because a fixed mass of gas can be compressed, gas must be made of particles, or atoms, because there is space between them. -
Lavoisier
Antoine Lavoisier and the Atomic Theory. Born in 1743, Antoine Lavoisier is credited as being the first person to make use of the balance. He was known for his skills in experimentation and loved to separate the oxygen molecule from HgO. This led him to come up with the Law of Conservation, which states that matter is unable to be made or destroyed. -
John Dalton
Beyond creating a model for atomic interactions, John Dalton is also credited with developing laws for understanding how gases work. In time, this would lead him to conclude things about how atoms interacted, the weight of atoms. -
Solid Sphere of "Billiard Ball" Model
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J.J. Thompson
In March, 1904, JJ Thomson proposed a model of the atom whereby the negatively charged corpuscles (electrons) were distributed in a uniform sea of positive charge and electrostatic forces determined their position. Known as the Plum Pudding Model, it played an important role in the research of atomic structure. -
Robert Millikan
Robert Millikan's primary contribution to atomic theory came as a result of his oil-drop experiment, which measured an electron's charge. Previously, J.J. Thomson had suggested the hypothesis that an electron's mass was at least 1,000 times less than the mass of the tiniest atom. Millikan's contribution to this hypothesis was to specify the size of the electron's charge. -
Dmitri Mendeleev
He is best remembered for formulating the Periodic Law and creating a farsighted version of the periodic table of elements. He used the Periodic Law not only to correct the then-accepted properties of some known elements, such as the valence and atomic weight of uranium, but also to predict the properties of eight elements that were yet to be discovered. -
The Curies
Atomic Theory of Matter Ninety years later, Pierre and Marie Curie were to discover and isolate radium, a new element which spontaneously disintegrated into other elements. This proved that the atoms of one element at least were not indivisible. -
Ernest Rutherford
in 1904, which suggested, upon Rutherford's 1911 analysis, that J. J. Thomson's plum pudding model of the atom was incorrect. Rutherford's new model[1] for the atom, based on the experimental results, contained new features of a relatively high central charge concentrated into a very small volume in comparison to the rest of the atom and with this central volume also containing the bulk of the atomic mass of the atom. This region would be known as the "nucleus" of the atom. -
"Plum Pudding" Model
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Henry G.J. Mosely
English physicist who experimentally demonstrated that the major properties of an element are determined by the atomic number, not by the atomic weight, and firmly established the relationship between atomic number and the charge of the atomic nucleus -
Neils Bohr
Bohr developed the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level (or orbit) to another. -
Solar System Model
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Werner Heisenberg
Werner Heisenberg contributed to atomic theory through formulating quantum mechanics in terms of matrices and in discovering the uncertainty principle, which states that a particle’s position and momentum cannot both be known exactly. The combined uncertainty in both measurements must be equal to or greater than h/(4π), where h is Planck’s constant. -
Electron Cloud Model
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Albert Einstein
Einstein's biggest contribution to the Atomic Theory was that he was able to fully prove through usage of evidence that atoms did indeed exist, and he was also able to demonstrate that electrons could leave metal through usage of light. He also created the mass energy equivalence equation, and this paved the way for the creation of the atomic bomb. -
The Alchemists
Alchemists also contributed to the atomic theory because of their studies of natural processes. Because the goal was to change items, the alchemists heavily studied fermentation, distillation, sublimation, and calcination.
