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Aristotle's theory of the atom was that it was made of the four elements: air, earth, water, and fire. Also he believed that there were four qualities to the elements: dryness, hotness, coldness, and moistness. In his model of the atom, the two forces were conflict and harmony. Conflict was supposedly causing bad things and harmony was causing good things. He did not like the idea of the atom being the smallest component of matter.
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He was the first person to come up with the idea of an existence of an ultimate particle. Democritus used the word "atomos" to describle the particle. He said everything is composed of atoms which are physically but not indivisible. Also he said that atoms are indestructible and will always be in motion.
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Antoine was the first person to make good use of the balance. He experimented a lot. After a visit with Priestly, he studied the burning process. He proposed the Combostion theory and named Oxygen. He also proposed the law of Conservation of Mass.
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John Dalton's theory stated that atoms cannot be created or destroyed. Also he said that they get rearranged in a chemical reaction. He also said that atoms of an element can combine with other atoms to make a chemical compound
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He studied the effect of X-rays on photographic film. Henri discovered some chemicals spontaneously decompose and give off very pentrating rays. He also discovered radioactive elements.
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He identified the negatively charged electron. He said that the electron was a component of all matter. He proposed the "Plum Pudding" model that showed the volume of the atom is composed primarily of the more massive positive portion. He also figured out what was called later on a "proton".
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Marie studied Uranium and Thorium and called their decay process "radioactivity". She and Pierre later on discovered other elements. The discovery of radioactivity by Henri Becquerel in 1896 inspired Marie and her husband in their researches and analyses which led to the other element discoveries.
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Bohr took advantage of Rutherford's experiment and Plancks beginnings at Quantum Theory and figured out distinct energy levels where electrons could exist. He said higher energy levels could only be obtained by electrons if they were excited. Later on, he figured out that Planck's constant determined the diameter of the atom.
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He used the ideas of quanta, which are discrete units of energy, to explain hot glowing matter. He also made a "Saturnian" model of the atom and it had flat rings. He worked a lot with radioactivity and radiation.
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He proposed the nuclear atom as the result of the gold-foil experiment that was conducted. Rutherford said that all the positive charge and all mass of the atom occupied a small volume at the center of the atom and most of the volume of the atom was empty space occupied by the electrons. He also referred to the hydrogen nucleus as a proton.
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Mosely figured out that the energy of x-rays emitted by the elements increased in a linear fashion with each successive element in the periodic table. He said the relationship was a function of the positive charge on the nucleus. This completely rearranged the periodic table by using the atomic number instead of atomic mass to represent how the elements progress.
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He described atoms as a formula connected to the frequencies of spectral lines. He also said you cannot know the position and velocity of a particle. Heisenberg is well known for quantum mechanics and the uncertainty principle in the atomic world.
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He determined the unit charge of the electron. He did an oil drop experiment at the University of Chicago to figure this out. This allows for the calculation of the mass of the electron and the positively charged atoms.
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Schrodinger saw electrons as continuous clouds. He also introduced "wave mechanics" as a mathematical model of the atom. He focused a lot on the old quantum theory which was developed by Planck, Einstein, Bohr, etc.
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He was mainly known for discovering the neutron. He worked with Rutherford's ideas, and James discovered fission. A devastating discovery that affected millions of peoples' lives later on, was his discovery of the atomic bomb
