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492 BCE
Democritus
His greatest contribution is his belief that everything in the world consists of particles called atoms. He believed those atoms are indestructible, indivisible, and always in motion. The atoms are infinite in numbers, come in different sizes and shapes. -
424 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 as that the form elements had the shapes fire(tetrahedron), air(octrahedron), water(icosahdren), and earth(cube). -
400 BCE
The Alchemists
They used Artistotle's ideas abut matter and began experimenting with them by treating different metals. They failed. They then created a scientific process which would follow for the eventual discovery of the atom -
340 BCE
Aristotle
Aristotle believed that it was possible to determine which substances contained more or less of each element based on its structure, design, and composition. He taught that there were four different category descriptions that would indicate the presence of one element more than another. The categories were hot, dry, cold, wet -
Robert Boyle
Best known as "The Father of Chemistry" for his discovery that atoms must exist based on the the relationship between pressure and volume of gas. His theorem called Boyle's Law reasons that because a fixed ass of gas can be compressed, gas must be made of particles, or atoms, because there is space between them. Boyle's discoveries helped bring chemistry into the modern age. -
Antoine Lavoisier
Lavoisier's most important contribution to chemistry by developing the law of conservation of matter. The law determined that combustion and respiration are caused by chemical reactions with oxygen, and helped systematic chemical nomenclature. -
John Dalton
Dalton's atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass. -
Dmitri Mendeleev
Mendeleev's greatest contribution to the atom is him creating the first periodic table of elements. The order of the elements in the table is determined by atomic mass. -
J.J. Thomson
Thomson is credited with the discovery of the electron and proving the existence of sub-atomic particles in an atom. Thomson used cathode ray tube, and demonstrated that cathode rays were negatively. -
Albert Einstein
Einstein's biggest contribute to the atomic theory was that he was able to fully prove through usage of evidence that atom did exist, and he was also able to demonstrate that electrons could leave metal through usage of light. -
Ernest Rutherford
Rutherford's atomic theory was that an atom had a central positive nucleus with negative electrons orbiting it. He developed this theory with his gold foil experiment. Resulting in the gold foil experiment Rutherford created the theory that stated that most of an atom was empty space. -
Robert Millikan
His main contribution to the atomic theory was deducing the electric charge of an electron. This discovery was made from his famous Oil drop experiment. In the experiment he switched oil instead of water in his atomizer -
Niels Bohr
Bohr's greatest contributions to modern physics was the atomic model. The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. Bohr was the first to discover that electrons in the outer orbit determined the properties of an element. -
Henry G.J. Moseley
He experimentally demonstrated that 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 -
Werner Heisenberg
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. He also worked on the theory of the atomic nucleus following discovery of the neutron, developing a model of proton and neutron interaction an early description of what decades later came to be known as the strong force.
