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Democritus
Democritus was a Greek philosopher who 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. -
John Dalton
John Dalton was an English chemist. His ideas form the atomic theory of matter. His ideas is that all matter is made of atoms. All atoms of a given element are identical in mass and properties. Compounds are formed by a combination of two or more different kinds of atoms. And the last idea he had was that a chemical reaction is a rearrangement of atoms. The last idea he had is that atoms of different elements are different not the same. -
J.J. Thompson
J.J. Thompson was English scientist. He discovered the electron when he was experimenting with gas discharge tubes. He noticed a movement in a tube. He called the movement cathode rays. 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 called electrons. -
Lord Ernest Rutherford
Ernest Rutherford conducted a famous experiment called the gold foil experiment. He used a thin sheet of gold foil. He also used special equipment to shoot alpha particles at the gold foil. Most particles passed straight through the foil like the foil was not there. Some particles went straight back or were deflected. The experiment shows that atoms are made of a small positive nucleus, positive nucleus repels positive alpha particles.
https://www.youtube.com/watch?v=ecsgC1wSp5I -
Niels Bohr
Niels Bohr proposed a model similar to the solar system. The electrons go around the nucleus like planets orbit around the sun. All electrons have their own energy level. The first level can hold 2 electrons, the second level can hold 8 electrons, the third level can hold 18 electrons and the fourth level can hold 32 electrons. The energy of electrons goes up from level 1 to other levels. When electrons release energy they go down a level. When electrons absorb energy, they go to a higher level.
