2. Once upon a time there was an ancient Greek philosopher named Democritus . Democritus discovered the atom. He said, “All matter is composed of atoms!” This was the first mention of matter being composed of invisible particles (atoms). He preformed no experiments, had not model, and little evidence.
3. Next, a man named John Dalton viewed the atom as a tiny, solid sphere. He learned that elements consist of atoms and he learned the masses of elements. Dalton wondered how water and air occupy the same space at the same time when bodies couldn’t. He preformed many experiments on the mixtures of gases. John Dalton’s model of an atom.
4. Later, J.J. Thomson discovered electrons (negatively charged particles). He learned through experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube. He found evidence of something smaller than an atom because of the deflection of rays by electrically charged plates and magnets. ( Thomson’s model )
5. Then Ernest Rutherford came up with an atom having a positively charged nucleus. He learned that most of the mass was in the nucleus and the rest of the atom was empty space. Ernest Rutherford preformed the gold foil experiment. He fired radioactive particles through minutely thin metal foils and detected them using screens coated with zinc sulfide. He found that about 1 in 8000 particles deflect leading him to believe that most of the atom was empty space. (Rutherford’s model)
6. Later on, Niels Bohr came up with electrons traveling in circular orbits and only certain orbits are followed. His theory became the basis for quantum mechanics. The stationary orbits were defined by their angular momentum. (Bohr’s model)
7. After Bohr’s knowledge, Erwin Schrodinger came up with the electron cloud. He viewed atoms as “layers within layers”. His idea was the first to involve particle waves. (Schrodinger’s model)
8. Finally! James Chadwick discovered the neutron. This takes us to the current model. The neutron is a neutrally charged particle. In the model, these particles are placed in the nucleus. (Chadwick’s model)