-
500
Democritus' Theory of the Atom
Around 500 B.C. Democritus and Leucippus developed the theory of Atomism. Leucippus is credited with developing it first.Their theory of the atom answered mechanistic questions (what earlier situations would have caused this?) opposed to teloelogistic questions (what was the purpose of this experiment?). A lack of technology led them to infer that atoms of the same material fit together to make said materials. Their theory was not widely accepted at the time because of its complexity. -
500
Aristotle's Atomic theory
Aristotle's theory of the atom was widely accepted for its simplicity and easily-grasped concepts. It answered the question of what is everything made up of and how small is the smallest particle. He claimed that everything is made up of four elements: earth, wind, water and fire and these elements are acted upon by the forces gravity and levity. his hypothesis also stated these elements were infinitely divisible. -
John Dalton's Atomic theory
Dalton created five points to his atomic theory: 1. elements are made fo small particles called atoms 2. atoms of the same element are identical 3. atoms cannot be created on destroyed 4.atoms of different elemnts combine to create chemicl compounds 5. in chemical reactions atoms combine, separate or rearrange. This answered the question: what makes up elements and what makes up compounds? -
Henri Bercquerel's Atomic theory
Henri Bercquerel studied the effect x-rays had on photographic film and discovered that elements can decompose spontaneously and release incredibly penetrating rays. His experiment answered the question: what creates x-rays and how? -
Marie & Pierre Curie's discoveries in Radiation
Marie and Pierre's discoveries were based off of Bercquerel's work with x-rays and helped lead them to finding two new elements: Polonium and Radium. While studying a sample of Uranium-containing ore and pure Uranium they noticed that the ore release a higher level of radioactivity than the pure Uranium, this in turn paved the way for them to find Polonium Radium. This answered the question of: why might a combined substance emit more radioactivity than a pure substance? -
J.J. Thomson's Atomic theory
Thomson's discovery of the atom lead him to experiment with the cathode ray tube. After sending an electric current through a vacuum tube, Thomson noticed a glowing light inside the tube. To find what was causing the glowing, he placed two electric plates in the path of the light, one negatively charged and the other positively charged. The light bent towards the positively charged plate, and he found that the particle creating this glowing light was the electron. -
Quantum Model/the current Atom Model
The Quantum model was created by Niels Bohr and consists of four numbers: the principal quantum number, the angular momentum quantum number, the magnetic quantum number and the spin quantum number. In a nutshell, these all together confirm the quantum theory: it is impossible to know the precise position and momentum of an atom and this theory is based on probability more than certainty. This principle is called the "Uncertainty Principle" because it is based on theory only, but it holds true. -
Ernest Rutherford Atomic Theory
Rutherford used his Gold Foil experiment to prove the existence of alpha particles. By aiming a beam of radiation through a slit in a lead shield and a sheet of zinc sulfide-coated screen lined the inside of this shield to make it fluorescent to pick up the alpha particles. Most of the alpha particles passed throughthe gold foil, and so he could infer that atoms are made up of a large amount of space. This answered the question: what takes up the area of empty space in an atoms e- cloud? -
Neils Bohr's Planetary Model
Borh's studies of the atom and mostly the electron led him to infer that the electron orbits the nucleus of an atom, but unlike Maxwell's equation, Bohr stated that the electron continously remained in orbit and did not emit any radiation and therefore would neither slow nor collide with eachother or the nucleus. His Discovery answered the question: does an electron give off radiation, and if not, why? -
Robert Millikan's Oil-Drop Experiment
Millikan determined the electric charge of one elctron by using oil and a specially made electric chamber to find out how strong of an electric field was needed to keep the drop from falling. From this he found the gravitational force on the drop and what its charge was and found that a charge on one drop was -1.6x10^-19 Coulombs (C). This answered the question of: what the charge of an electron? -
James Chadwick discovery of the Nuetron
Chadwick, under the wing of Ernest Rutherford, began theorizing about a neutral part of the nucleus of an atom that contained mass but no charge. His theory was widely acccepted although it was never truely proved or discovered. This answered the question: is there a section of the atom neither negatively nor positively charged, and only measured in mass? this discovery paved the way for the use of the uranium atom and splitting atoms to release a massive amount of energy.
