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Democritus
He proposed the idea that matter is made of tiny, indivisible, indestructible particles that he called atomos, from which the English word atom is derived. He didn't have the necessary equipment to test his ideas by using controlled experiments, and his ideas were eventually rejected.https://www.youtube.com/watch?v=IO9WS_HNmyg -
John Dalton
He thought all elements are composed of atoms. He said that all atoms of the same elements. Atoms of different elements are different. Atoms of different elements combine to form a compound. These atoms have to be in definite whole number ratios. Those were Dalton's ideas to form the atomic theory of matter. https://www.youtube.com/watch?v=OUoV--CuLDA -
J. J. Thomson
He discovered the electron when he was experimenting with gas discharge tubes.He noticed a movement in a tube. The rays moved from the negative end of the tube to the positive end. He realized that the rays were made of negatively charged particles-electrons. https://www.youtube.com/watch?v=JwdGFZA3WOs -
Lord Ernest Rutherford
He conducted an experiment called the gold foil experiment. He used a thin sheet of gold foil. He also used special equipment to shoot alpha particles, (positively charged particles,) at the gold foil. Most particles passed straight through the foil like it wasn't there. Some particles went straight back or were deflected as if they had hit something. The experiment showed that atoms are made of small positive nucleus and atoms are mostly empty space.https://www.youtube.com/watch?v=45TGJRBFLNc -
Niels Bohr
He proposed a model of the atom that was similar to the model of the solar system. The electrons go around the nucleus like planets in its orbit around the sun. All electrons have their energy levels which is a certain distance from the nucleus. Each energy level can hold a certain amount of electrons. Level 1 can hold 2 electrons, level 2 can hold 8 electrons, level 3 can hold 18 electrons, and level 4 can hold 32 electrons. https://www.youtube.com/watch?v=nVW1zDPPZGM
