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450 BCE
Democritus
A greek philosopher who figured out that all matter around us is made up of tiny particles -
427 BCE
Plato
Plato theorizes that these solid forms of matter are composed of indivisible elements shaped like triangles -
760
The Alchemists
Mercury and sulfur were the metals from the two principles. -
Robert Boyle
demonstrating that matter is made of tiny particles that he called corpuscles, but that are known as atoms today. He also made the Boyle law which discovered the inverse relationship between pressure and volume in a gas. -
Antone Lavoisier
A French chemist who found modern chemistry with the concepts that an element cannot be broken down into smaller components and that combined elements create chemical compounds. -
John Dalton
Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. -
Billard Ball Model
This was Dalton's theory, a theory of chemical combination. He defined an atom to be a ball-like structure, when the concepts of atomic nucleus and electrons were not known at the time. -
Amedeo Avogadro
explained experimental data on chemical reactions by proposing that equal gas volumes contain equal numbers of molecules, under the same conditions of temperature and pressure. -
Dmitri Mendeleev
A Russian chemist who created the periodic table -
JJ Thompson
Discovered the electron. He also studied canal rays found that they were associated with proton H+ -
Marie Curie and Pierre
French physicists Pierre and Marie Curie discovered the strongly radioactive elements polonium and radium, which occur naturally in uranium minerals. -
Plum Pudding Model
In Thomson's plum pudding model of the atom, the electrons were embedded in a uniform sphere of positive charge. -
Albert Einstein
Publishes theory on special relativity and states that matter can be converted into energy. -
Robert Millikan
Performed an oil drop experiment to determine the charge and the mass of an electron. -
Ernest Rutherford
Performed the gold foil experiment to determine that the nucleus is a small, dense, and positively charged part of the atom, based on the assumption that electrons are on the outside of the nucleus. Develops the plum pudding model of the atom. -
Solar System Model
The Solar system model or the Bohr model of the atom describes atoms as consisting of a nucleus with a number of electrons in orbits around that nucleus, similar to a solar system. -
Henry G. J. Mosely
discovered that the number of protons in an element determines its atomic number. -
Electron Cloud Model
The electron cloud model shows a particular area in which an electron is likely to be. -
Erwin Schrödinger
Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom. -
James Chadwick
Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Discovered it as the neutron.