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100
Alchemists
Around 100 BC, a group referred to as the alchemists that lived in the East around that time. They further developed Aristotle's theory on the four elements and attempted to record what everything was made of pertaining to these elements. Their ideas were created after both Aristotle and Democritus. -
340
Aristotle
Aristotle taught a theory all over Athens that everything was made of the four elements: fire, water, earth, and air. This theory was later proven wrong. His theory was found later than Democritus', but the BC time will not show it that way on the timeline. -
400
Democritus of Adbera
Democritus had five parts to his theory about atoms: all matter is made of atoms, atoms are indestructible, atoms are solid amd invisible, atoms are homogenous, and that atoms differ in size, shape, mass, position, and arrangement. He also thought that solids were made of pointy atoms, liquids were made of round atoms, and oils were made of very small atoms. The image is of what Democritus thought an atom looked like. He discovered his theory before Aristotle but the timeline doesn't show it. -
Benjamin Franklin
Franklin's most famous experiment with a kite led him to the discovery that atoms have charges. Franklin tied a key to a kite during a thunder strorm, which then got struck by lightning. -
Antoine Lavoisier
Lavoisier found that mass is conserved during chemical reactions, leading to the creation of the law of conservation of mass. This law states that no mass is gained or lost during a chemical reaction. -
Joseph Proust
Proust created the law of definite proportions, stating that the ratio of elements in a compound always remains the same. -
John Dalton
Dalton's atomic theory had four parts: all matter is made of indivisible and indestructable atoms, all atoms of an element are identical in mass and properties, compounds are made of multiple types of atoms, and that a chemical reaction is simply a rearrangement of atoms. -
Michael Faraday
Michael Farday placed two electrodes in water containing a dissolved compound and found that one of the elements was drawn to one of the electrodes and the other was not. He discovered that there were electric forces at play in atoms. -
James Clerk Maxwelll
Maxwell created a theory on electromagnetism. He related waves to electromagnets ivolving the velocity of light. His ideas predicted the frequency at which light shuold be emited from a charged particle orbits around an oppositely charged particle in the atom. -
Dmitri Mendeleev
Mendeleev created a periodic table containing elements and arranged them based on their atomic mass. He used the patterns he saw among atoms to create this table and simplify the atomic theory. -
G. J. Stoney
From data collected from the electrolysis of water and the kindetic theory of gases, Stoney found the magnitude of the electron. He also named the electron. -
William Crookes
While studying what happened to an electric current send into a gas in a sealed tube, Crookes discovered the cathode and the cathode ray. These particles were first believed to be negatively charged atoms. -
Eugen Goldstein
Goldstein discovered what he called canal rays, rays that travel in the opposite direction from cathode rays. The rays he discovered traveled from the anode to the cathode. He found that these particles must have the opposite charge of the cathode rays since they travel in the opposite direction. -
Wilhelm Roentgen
Roentgen discovered x rays through his experimentation with cathode rays. These rays were originally known as Roentgen rays. -
Henri Becquerel
Becquerel was the first to discover radiation. He found that some chemicals spontaneously decomposed and gave off penetrating rays. -
Joseph John Thomson
Thomson discovered the electron, a particle within the atom with a negative charge. He created a model of the atom with both positive and negative charges. -
Marie and Pierre Curie
Throught their studies on radiation, the Curies discovered that pitchblende contained a small radiating element. Through this idea they found two new radiating elements. -
Max Planck
Planck founded the quantum theory, thinking that pockets of light and energy were found in quantums. This was the first idea in finding the quantum world. -
Frederick Soddy
Soddy thought that there were different forms of every element with a different number of neutrons. Soddy created an early theory on isotopes. -
Hantaro Nagaoka
Discovered the first quasi-planetary model of the atom. He thought that the atom had a large positively charged center and was surrounded by negatively charged light weight particles. -
Richard Abegg
Abegg discovered that the noble gases were stable because each of them contained eight electrons on their outer most shell. He then proposed the valence bond theory. -
Albert Einstein
Einstein published his famous theory of relativity contradicting the wave theory of light. -
Robert Milikan
Milikan discovered the charge of an electron by his oil drop experiment. In this experiment he put a charge on a drop of oil to see how stron an electric field mst be in order to stop the drop from falling. -
Ernest Rutherford
Rutherford was a New Zealant physicist that discovered the atomic nucleus through his experiement with gold foil in which he found the nucleus and developed an updated model of the atom. -
Niels Bohr
Bohr discovered a theory off of the quantum theory: he thought that energy is only transferred in certian definite quantities and that electrons move around the nucleus in certain, defined paths. -
Francis William Aston
He discovered a large number of isotopes using a mass spectrometer. -
Louis deBroglie
DeBroglie created a theory of electrons waves stating that matter on an atomic scale could have the same properties as waves. -
Werner Heisenberg
Heisenberg described atoms with a formula connected to the frequencies of spectral lines. He also found the position priciple of inteterminary stating that one cannot know both the position and velocity of an atom. -
Paul Dirac
Dirac created the dirac equation, which describes the behavior of fermisions like an elecetron. This equation also predicted antimatter. -
Erwin Schrödinger
Schrödinger thoguht that electrons were continuous clouds, introducing wave mechanics through his mathematical model of the atom. -
James Chadwick
Chadwick discovered the nuetron after hearing of the discovery of the proton. He also won a nobel prize for this discovery. -
Glenn Seaborg
Seaborg was involved in finding nine transuranium elements.
