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Atom, Models of an Atom, He proposed that all matter is composed of small…

- - - - Leucippus, a Greek philosopher, is deemed the originator of the theory of atomism, which states that everything in the physical world is made up of an infinite number of indivisible particles that are not visible to the human eye because of their small size
      - Democritus' Concept of the Atom (430 BCE)
        
        Plato's Concept of the Atom (427 BCE)
        
        Aristotle's Concept of the Atom (300s BCE)
        
        There are only five solid shapes whose sides are made up of regular polygons, according to Plato (triangles, squares, pentagons, hexagons, etc). Plato was so taken aback by this discovery that he believed all matter atoms descended from these five fundamental solids. He proposed the atomic theory, in which ideal geometric forms are used to represent atoms.
        
        Aristotle did not believe in the atomic theory and did not teach it. He believed that all materials on Earth were made out of the four elements, Earth, Fire, Water, and Air, rather than atoms. He believed that all substances were made up of trace amounts of these four matter elements.
        
        Democritus, a student of leucippus, claimed that atoms were uniform, solid, hard, incompressible, and indestructible. He also believed that they moved in infinite numbers through an empty space called the void until stopped.
- - - - Gold Foil Expermient
      - Proton (1919)
        
        Neutron (1932)
        
        Bombarded Beryllium with alpha particles from the natural radioactive decay of Polonium