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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 (meaning indivisible) is derived. He did not 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 form the atomic theory of matter.His theory's name was Dalton's Atomic Theory. His theory was that all elements are composed of atoms.It is impossible to divide or destroy them.Another one of Dalton's ideas was that all atoms of the same elements.For example, one atom of oxygen is like another atom of oxygen.Lastly his idea was that a chemical reaction is a rearrangement of atoms.link text -
J.J Thompson
J.J Thompson was also a English Scientist. There wasn't a name for his theories. He discovered the electron when he was experimenting with gas discharge tubes. Then 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- electrons. Link text -
Lord Ernest Rutherford
Ernest Rutherford conducted a famous experiment called the gold foil experiment. He used 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 the foil was not there. Some particles went straight back or were deflected (went in another direction) as if they had hit something. Atoms are mostly empty and atoms are made of small positive nucleus. -
Niels Bohr
Niels Bohr was a Danish physicist, He proposed a model of the atom that is similar to the model of the solar system. The electrons go around the nucleus like planets orbit around the sun. All electrons have their energy levels. Each energy level can hold a certain number of electrons. When electrons release energy they go down a level. When electrons absorb (gain) energy, they go to a higher level.
