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400
Democritus (400 B.C.)
Democritus stated that matter have a small particles which cannot be divided. He called them atomos which means not divisible. According to his theory atoms are the building blocks of matter and indestructible. He also said that atoms shape can change. -
Dalton's Atomic Theory
John Dalton stated that atoms are indivisible and have their own characteristic properties. He found that atoms with same characteristics forms elements and atoms with different characteristics forms compounds. He also tought that atoms were sphere. -
Thomson's Atomic Theory
J.J. Thomson tought atoms as plum pudding. He stated that atoms are big sphere with positive charges (the plum pudding) and have small negative charges in them (raisins in the plum pudding). He also found that the negative charges carried by electrons are egual to positive charge.
https://www.youtube.com/watch?v=RW_zfKOU9uM -
Rutherford's Atomic Theory
Ernest Rutherford shot some alpha particles to gold foil. He saw that most of the particles passed the foil. He stated that the electrons are around of the nucleus. He also found that an atom is mostly an empty space.
https://www.youtube.com/watch?v=Zd6_zVdMgJk -
Bohr's Atomic Theory
Niels Bohr stated that electrons are orbiting the nucleus with specific energy levels. Which means electrons have fixed steps. He found that electrons can't be in the space between orbits. He tought atoms as mini solar systems.
https://www.youtube.com/watch?v=Ic8OnvRonb0 -
Modern Atomic Theory
This is the atom model we know today. James Chadwick found neutrons. As we know today the movement of electrons can only be found by complex mathematical equations with the help of quantum mechanics.
