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200
Aristotle
Aristotle-Another philosopher in Greece, Aristotle didn’t like the atom as a round substance that couldn’t be split any more. So he made an atom by his own logic and reasoning probably around 350 BC. The only reason why it overcame all other theories is that people liked Aristotle’s philosophies better. The atom he made was based on four elements Earth, Fire, Air, and Water with Dryness, Hotness, Wetness, and Coldness in between them. -
201
Democritus
Democritus- Democritus was a philosopher in Greece who lived 2 generations before Aristotle. He got the idea of an atom from seeing that when a substance is divided in half, it’s still the same substance. So in 422 BC Democritus wondered what the smallest a substance could be. So he came up that there are different kinds of atoms which vary in size, round, always moving, and are indestructible. -
Antoine Lavoisier
Antoine Lavoisier-Lavoisier was a French chemist who experimented with calx of mercury and found that the combined mass of the mercury and oxygen separated was the same mass as the mass of the calx of mercury before separating them. This way he created the law of conservation of mass and the first list of elements. He didn’t really have an atom model but his work helped Dalton form his atomic theory. -
John Dalton
John Dalton-Dalton was an English chemist and physicist who was curious about elements in Lavoisier’s experiments and decided to investigate himself. The result was his atomic theory that says the atoms of the same elements are matching, atoms of different elements have different masses, and compounds are made of different elements bonded together. -
Henri Becquerel
Henri Becquerel-Becquerel was a French physicist who discovered radiation. He discovered by accident when he was experimenting with x-rays and photographic film that invisible rays were emitted. This showed that atoms weren’t as stable and indestructible as people thought. -
J.J. Thomson
J.J. Thomson-Thomson was an American scientist who discovered his part by using a Crook’s tube and positively and negatively charged plates. He then found when he sent a beam of electrons through the tube; the beam was attracted to and bent toward the positive plate, proving that the beam was negatively charged. So J.J. Thomson created a model of his own understanding: the atom is a sphere with negatively charged electrons located randomly in the sphere and to cancel the negativity the rest of t -
Curies
Curies-the Curies are chemists-physicists who studied the radioactivity of uranium and discovered two other radioactive elements polonium and radium. This further showed that more than one element can be unstable. -
Max Planck
Max Planck-Planck was a German physicist who came up with the quantum theory. This theory said that when energy enters a particular atom and is finally released, the atom produces a specific color to that atom in our eyes. In the invisible spectrum the particular atom releases a specific frequency of waves; using this we can identify particular atoms just by their frequency. Later we discover that this is caused by electrons jumping between electron layers. -
Robert Millikan
Robert Millikan- Millikan was an American physicist who discovered the charge of the electron. He performed an experiment with a charged drop of oil to see how strong an electric field had to be to stop it from falling. He then did more experiments with oil drops that were more charged and discovered that they were all a multiple of -1.6 x 10^-19 C which was the charge on a single electron. -
Earnest Rutherford
Ernest Rutherford-A a student of J.J. Thomson, Rutherford was a New Zealand physicist who explained what the results of the gold foil experiment. Geiger and Marsden focused a gamma ray at the gold foil but then surprisingly some of those particles would bounce off of the gold. Rutherford then decided that there's a positively charged concentrated mass in the center of the atom. This contradicts the “plum pudding” model because if it was true gamma particles would have gone straight through. -
Niels Bohr
Niels Bohr-Bohr was a Danish physicist who was a student to both J.J. Thomson and Rutherford. He studied the quantum theory and figured that atoms have electron levels in order to be able to release energy the atom pent up when it was excited. It has neutrons and protons in the center and electrons in electron shells that can only hold a specific amount of electrons. This enhances Rutherford’s model by the knowledge of where the electrons are. -
Henry Moseley
Henry Moseley-Moseley, an English physicist, found that the energy of the elements coming out from x-rays increased linearly. This meant that the number of protons in elements increased by one the more complex the atom got. This changed the periodic table to one that used the atomic number instead of the atomic mass. -
Erwin Schrodinger
Erwin Schrodinger-Schrodinger was an Austrian physicist who found that within electron shells, there are subshells where the first one has one, second two, third three, etc. Within the subshells there are orbitals which are a space where two electrons could be. It enhances Bohr’s model by making the placement of the electrons more specific. -
Werner Heisenberg
Werner Heisenberg-Heisenberg was a German physicist who was a student under Niels Bohr. He created the Uncertainty Principle which means "The more precisely the POSITION is determined, the less precisely the MOMENTUM is known." -
James Chadwick
James Chadwick-Chadwick, an English physicist who worked with Rutherford and discovered the neutron.
