-
370
Democritus died
BCE -
460
Democritus was born
Abdera, Thrace (BCE)
fifth century B.C. hypothesized that all matter (plus space and time) is composed of tiny indestructible units, called atoms.
The first one to really theorize about atoms and their existence -
Period: 460 to
Atomic Theory
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John Dalton was Born
Cumberland, England CE.
His atomic theory said that elements consisted of tiny particles called atoms. It states an element is one of a kind (aka pure) because all atoms of an element are identical. All the atoms that make up the element have the same mass. All elements are different from each other due to differing masses. They are not easily separated from one another. Compounds have a fixed ratio of atoms. Each atom has its own characteristic weight, creating a weight ratio between elements. -
Sir William Crookes was Born
London, England CE -
John Dalton Died
Manchester, England CE -
JJ Thomson was Born
J.J. Thomson discovered electrons and noticed that an atom can be divided. Also, he concluded atoms are made of positive cores and negatively charged particles within it. He developed the Plum Pudding Model before the atomic nucleus was discovered. This model shows that the electrons are surrounded by a "pudding" of positive charges to balance the negative charges. -
Max Planck was Born
Kiel, Germany
In 1901 he devised a theory that perfectly described the experimental evidence, but part of it was a radical new idea: energy did not flow in a steady continuum, but was delivered in discrete packets
received the Nobel Prize in 1919 -
Robert Millikan was Born
Born in Morrison, Illinois. His earliest major success was the accurate determination of the charge carried by an electron, using the elegant "falling-drop method"; he also proved that this quantity was a constant for all electrons (1910),
Next, he verified experimentally Einstein's all-important photoelectric equation, and made the first direct photoelectric determination of Planck's constant h (1912-1915). -
Ernest Rutherford was Born
Nelson, New Zealand. Created the "disintegration theory" of radioactivity which regards radioactive phenomena as atomic - not molecular - processes.In 1910, his investigations into the scattering of alpha rays and the nature of the inner structure of the atom which caused such scattering led to the postulation of his concept of the "nucleus". In 1919 he discovered that the nuclei of certain light elements, such as nitrogen, could be "disintegrated" by the impact of energetic alpha particles. -
Lise Meitner was Born
Vienna, Austria. In the summer of 1938, she went to Manne Siegbahn's institute in Stockholm.
On November 13, 1938, Hahn met secretly with Meitner in Copenhagen. At her suggestion, Hahn and Strassmann performed further tests on a uranium product they thought was radium. When they found that it was in fact barium, they published their results in Naturwissenschaften (January 6, 1939). -
Otto Hahn was Born
Frankfurt am Main, Germany
In 1938, Hahn and radiochemist Fritz Strassmann discovered nuclear fission. They were awarded the Nobel Prize in Chemistry in 1944 -
Albert Einstein was Born
Ulm, Germany
in 1905 proposed that light energy can be absorbed or emitted only in discrete packets called quanta
Einstein also in 1905 mathematically proved the existence of atoms
Einstein’s calculations were fully confirmed by Jean Perrin in 1909, winning Perrin the Nobel Prize. -
Crookes Study
Studied the effects of sending an electric current through a gas in a sealed tube. The tube had electrodes at either end and a flow of electrically charged particles moved from one of electrodes. This electrode was called the cathode, and the particles were known as cathode rays. The particles were believed to be negatively charged atoms or molecules. However,experiments showed that these particles could penetrate thin sheets of material which would not be possible if the particles were big. -
Niels Bohr was Born
Copenhagen, Denmark. In 1913, he passed on to a study of the structure of atoms on the basis of Rutherford's discovery of the atomic nucleus, and since 1920 (until his death in 1962) he was at the head of the Institute for Theoretical Physics, established for him at that university.
His work on the atomic structure, he succeeded in working out and presenting a picture of atomic structure that, with later improvements, still serves as clarification on the physical and chemical properties of the -
James Chadwick was Born
Cheshire england
Chadwick was most famous for his discovery of the neutron in an atom in 1932. -
Fritz Strassman was Born
Boppard, Germany
He earned his Ph.D. from the Technical University of Hannover in 1929
In 1966, for recognition of their work on nuclear fission, Strassmann, Hahn and Meitner shared the Enrico Fermi Award. -
Ernest Rutherford Died
died in Cambridge, United Kingdom. -
JJ Thomson Died
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Max Planck Died
Göttingen, Germany -
Robert Millikan Died
San Marino, California. -
Albert Einstein Died
Princeton, New Jersey -
Otto Hahn Died
Göttingen, Germany -
Lise Meitner Died
Cambridge, England. -
James Chadwick Died
Cambridge,Endinburg -
Fritz Straussman Died
Mainz, Germany. -
Aristotle was born
Stagira, Greece (BCE)
When the Atomic Theory was discovered, Aristotle did not believe in it. He believed that all substances were made of Fire, Water, Air, and Earth.
Setback atomic theory for almost 2000 years
