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400 B.C.E. What: He created the first atomic model. How: His model of the atom depended on analogies from human senses.
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400 B.C.E. What: He developed a theory that was based on the four elements. How: Aristotle’s theory made a great generalization of all matter of the four elements: fire, water, earth, and air. He also believed that there were four qualities to these elements: dryness, hotness, coldness, and moistness.
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What: Proposed his modern theory of the atom. How: He based it upon : 1. Matter is made up of atoms that are indivisible and indestructible. 2. All atoms of an element are identical. 3. Atoms of different elements have different weights and different chemical properties. 4. Atoms of different elements combine in simple whole numbers to form compounds. 5. Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged.
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What: He discovered the Plum Pudding Model of the atom. How: In J.J.'s model, the atom is composed of electrons surrounded by an area of positive charges to balance out the negative charges.
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What: Theorized that atoms have their positive charge concentrated in a very small nucleus. How: He pioneered the Rutherford model of the atom, with his discovery and interpretation of Rutherford scattering in his gold foil experiment.
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What: Presented a picture of an atomic structure. How: He passed on to a study of the structure of atoms based on Rutherford's discovery of the atomic nucleus. (This lead him to the picture of his atom.)
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What: He generated a mathematical model for the distribution of electrons in an atom. How: The solution to the Schrodinger Equation lead to Quantum numbers which provide the address of the electrons in an atom.
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Overview of the atomic theoryWhat: The foundations of Quantum Mechanics and the "cloud model" of the atom. THe Uncertainty Principle stated simplistically that the more precisely the position of an electron is determined, the less precisely the momentum (mass & velocity) is known in this instant, and vice versa.
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What: He proved the existence of neutrons. How: He heard of a new method of detecting particles emitted by radioactive elements developed by Irene Joliot-Curie.
