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460 BCE
Democritus
Democritus had an idea that matter is made of tiny,indivisible,indestructible particles called atoms. He did not have the necessary equipment to test his ideas by using controlled experiments, and his ideas were eventually rejected. https://www.youtube.com/watch?v=TgWn91ap99A -
John Dalton
Dalton's ideas formed the atomic theory of matter called Dalton's Atomic Theory. He said that all elements are made up atoms, an atom of hydrogen and an atom of carbon forms a hydrogen bond, compounds are made up of two or more different types of elements, and the ratio of atoms in HCl is 1:1. https://www.youtube.com/watch?v=QciVy2QSVwY -
Lord Ernest Rutherford
Rutherford conducted an experiment called the Gold Foil Experiment. It showed: Atoms are made of a small positive nucleus; positive nucleus repels positive alpha particles;and atoms are mostly empty because the particles would pass straight through the foil as if it wasn't there. https://www.youtube.com/watch?v=Q9zFWIfUHvc -
J.J. Thompson
Thompson discovered electron when he was experimenting with gas discharge tubes. The experiment showed: The charge of an electron was negative; cathode rays are made of electrons;and electrons move form the negative end of a tube to the positive end because and electron caries a negative charge and in electricity, opposites attract. https://www.youtube.com/watch?v=JwdGFZA3WOs -
Niels Bohr
Niels Bohr proposed a model of the atom that is similar to the model of the solar system. It could be called a planetary model of the atom because the electrons go around the nucleus like planets orbit the sun. Bohr discovered that electrons in the same atom differ because they have different energy levels and to jump to a level above them, the electron needs to absorb energy; and to jump to a level below them, the electron needs to release energy. https://www.youtube.com/watch?v=1b9UKTbjj7I
