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415 BCE
Democritus and the atom
Democritus was a Greek Philosopher. He proposed the conscience of matter being made up of "tiny, indivisible, and indestructible particles" which he named atomos, meaning indivisible. However, his ideas were soon rejected. -
John Dalton's Atomic Theory
John Dalton was a chemist. He formed an Atomic Theory, which contains five sectors.
1. All matter consists of tiny particles.
2. Atoms are indestructible and unchangeable.
3. Elements are sorted by the atomic mass of their atoms.
4. When elements react, their atoms join in simple, whole integer proportions.
5. When elements react, their atoms sometimes combine in more than one simple, whole-number ratio.
These sectors made the basis of atomic chemistry.
URL: http://antoine.frostburg.edu/ -
J.J. Thomson's Gas Discharge Tube Experiment/Discovering Electrons
URL: Electron Video
J.J Thomson performed his famous gas discharge tube experiment in 1897. He noticed a movement in his gas tube, and then recognized it as cathode rays. The ray that transferred from one end to the other end was named the electron. -
Lord Ernest Rutherford's Gold Foil Experiment
URL: Nucleus Video
Lord Rutherford was a chemist, and conducted the popular Gold Foil Experiment. This was an experiment, in which he used special equipment to blast particles called alpha particles, in order to see if they would pass through the foil instantly. It partially worked! He discovered two things:
1. Atoms are mostly empty space.
2. They are made of a small positive nucleus. -
Niels Bohr's Atom Model
Niels Bohr was a Danish physicist. He created a model of an average atom, which looked like a solar system. This was what he discovered: the levels where electrons bounce around.
Levels: 1- 2 electrons
2- 8 electrons
3- 18 electrons
4-32 electrons
