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460
Democritus 460-370 B.C
Democritus contributed to the history of the atom by creating the first atomic model. His thoery was that all atoms are made of small, indivisbible and indestructable particles called atoms. His model was very simple and the idea of electrons, neutrons, and protons were not yet introduced. He also believed that if matter were to be divided into smaller pieces you would end up with an atom. Known--> none -
John Dalton
John dalton Greatly contributed to the History of the Atom when he formulated the atomic theory, This theory stated three things, 1) Each element is composed of tiny indestructale particles called atoms, 2) All atoms of a given element have the same mass and other properties that distinguish them from other elements, and 3) Atoms combine in simple whole number ratios to from compounds. ( text Book ) His model of the atom was most similar to democritus`s model. -
Dmitri mendeleev
Demetri Mendeleev was a russian chemistry professor and the first to arrange the elements on what is known today as the periodic table of elements. He noticed that some groups of elements had very similar properties which led him to establish the periodic law. This states that "when elements are arranged in order of increasing mass, certain set of properties recur
( mendeleev). Known-> none -
J.J. Thompson
Thompson an english physicist discovered the electron, a small negativley charged particle, through the Cathode ray Tube exepriment. In the experiment he sent electrical currents through a vaccume tube, he then placed a positive and negative plate in the tube and found that the light would bend towards the positive plate therefore it must of been negativly charged. he also created the plum pudding model where negativly chraged electrons were held inside a positively charged shell. -
Robert Millikan
Rober Millikans contributed to the history of the atom by determining the charge of an electron using his Oil Drop experimnet. This experiment also proved that the charge and quantity is the same for all electrons. This made it possible to calculate the mass of an electron in an atom.
Known -> electron -
Ernest Rutherford
Ernest Rutherfrod worked unded J.J. Thompson and supported his Plum pudding theory of an atom. He is most wellknown for discovering the proton during an experiment that attempted to prove the plum pudding theory correct. In his Gold Foil experiment he sent alpha particles particles towards a thin sheet of gold, most of the particles passed through the sheet however some were diflected. This led him to believe that most matter was concentrated in the center of the atom the nucleus. Known-> Pr, El -
Henry Mosley
Henry mosley is well known for using X-ray spectrum to study wavelengths and determine the number of protons in an element. He Is also known for arranging the chemical elements in order of their atomic number in what is now known as the periodic table of elements. -
Niels Bohr
Bohr is most well known for his planetary model of the atom, an extension of rutherfords theory, where proton are in the nucleus and the electrons travel in a specific orbit around the nucleus. Each orbit has the ability to hold a certain number of electrons and that everytime an electron changes orbit, it emits energy.
Known-> protons, electrons, nucleus -
Erwin Schrodinger
Sschrodinger continued his work on Niels Bohrs model of the atom and he contributed to the history of the atom in the quantum mechanical model of the atom. In his model the electrons path is not defined and the exact location cannot be stated. His model focused on the probability of an electrons location. In his model there is a Nucleus which is surrounded by an electron cloud.
Known--> all -
James Chadwick
James chadwick contributed to the histroy of the atom when he discovered the Neutron. He also determined that the atomic mass was double the number of protons because protons and neutrons have reltivly similar masses.
Known-Proton,neutron, electron, Nucleus -
Aristotle 380-320 B.C
Aristotle contributed to the History of the atom early on. He Did not believe in the atomic Theory but rather that all matter on earth was made of four elements, Fire, Water, Earth, and Air. He believed that all substances on earth were made of different proportions of these four elements. At the time his theory was widley believed which lead people to dismiss democritus`s Atomic theory.
