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Period: 300 to
The History of the Atom Timeline
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340
Aristole
He found that matter is made of atoms. He also found that matter will always exist. He also found 4 elements, fire, water, earth, and air. With all this, he came up with the theory of motion -
400
Democritus
Democritus found that atoms are not all the same, they are eternal, and always moving. He made a theory on this to explain why and how atoms were so small, and what they were about. He proposed a more advance atomic theory. . He said all matter is composed of indivisible tiny things made up into small not being able to be seen by the eye structures. -
Period: 400 to
History of the Atom Timeline
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John Dalton
He proposed the atomic theory. He inferred proportions of elements in compounds. He found the atomic weight, and chemical symbols. He also had the most useful atomic theory of matter. To come up with this, he tested gases and used evaporation to find out what the gases had on that mixture all together -
Henri Becquerel
He came up with radioactivity. He found this out from unknown x-rays waves, which were produced by uranium. Penetrating radiation was also discovered by Becquerel. He also discovered that uranium was able to expose a photographic plate on black paper, and didn’t depend on the chemical state -
J.J. Tomson
He found electrons and subatomic particles when he was working with cathode ray tubes. He was working with glass tubes and electricity and messed up and discovered electrons. He said the atom was a sphere of positive electricity, with negative particles throughout. This came around right after he discovered the electron. -
Marie & Pierre Curie
They both picked up on Becquerel’s work on uranium, which lead them to find the elements radium and polonium. Though Marie went further with the radioactivity of elements, she didn’t get very far. All she said was, “they were somehow disintegrating over time and emitting radiation that exposed the plate.” Pierre went on to say that atoms might be composed of even smaller things. -
Robert Millikan
He was by far the most famous American scientist. He wanted to find the electrical charge of electrons. He measured water droplets, and that wasn’t successful, so he measured oil droplets, where all this proved electrons were negatively charged. He also was a professor for many years, and wrote many textbooks on chemistry. -
Ernest Rutherford
He ionized gas using radiation, and found alpha and beta waves. He used his research and the magnetic properties of iron to find radio waves. He also discovered the atomic nucleus using others research and findings. To find this he did the Rutherford experiment. Briefly, he used a thin foil made of gold metal to find positive and negative charges in an atom. -
Neils Bohr
Niels figured out the structure of the atom, and their radiations. He also discovered the principle of complementary. He introduced electrons from the book he wrote on the structure of the atom. He also started the basis of the quantum theory. Niels Bohr discovered this atom. It shows a positively charged nucleus surrounded by electrons. This was mostly to explain the Rydberg formula. The Bohr model is a hydrogen model. It helps with the learning of the quantum theory. -
THe Quantum Model
The quantum model is a probability area an electron may be located in. In 1923 Louis de Broglie suggested that an electron moves with a wavelength that completes a circle, which would explain the different energy levels as Bohr’s model did but would also explain the wave diffraction pattern obtained by C.J. Davisson and L.H. Germer. In 1925 Erwin Schrödinger developed his wave equation which explained the motion of the electron by taking into effect the forces surrounding the electron. -
James Chadwick
James discovered the existence of the neutron. He found this out because when he was looking at alpha waves, bounced off, saying there was no charge in the neutron. He also used an experiment similar to this to help with the creation of the atomic bomb, and the fission and uranium 235.
