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400
Democritus (400 BC)
Democritus was a Greek philosopher/scientist. He said that matter cannot be distryoed, and matter cannot be divided into smaller parts. He also named the atom, which is Greek for indivisible. -
Antonie van Leeuwenhoek
Antonie was the inventor of the microscope, and proved that bacteria exists. Also Antonie proved the existance of the cell. -
Isaac Newton
Newton formulated the laws of motion and universal gravitation which dominated scientists' view of the physical universe for the next three centuries. -
John Dalton
Jahn Dalton's atomic theory stated; all elements are composed of atoms which are indivisible and indestructable. All masses of the same element are exaclty alike, and all have the same mass. Atoms of different elements are different, and have different masses. Compounds are formed by joining the atoms of two or more elements. He also believed an atom is the smallest unit of an element that can exsit. -
William Crookes
William Crookes was an english chemist. He evacuated a Crooke's Tube, also known as the Cathode Ray Tube, and sent an electrical charge through it. He said that glass wall glows and that objects placed inside the tube creates a shadow. He also said there are particles traveling from the Cathode. Which would later be discovred as radiation. -
J.J. Thomson
J.J. Tomson modified Crooke's experiment by adding a magnietic feild. He stated when particles are excited/heated they give off particles which are smaller than atoms. Theses particles are attracted to a positivly charged object. He also stated that atoms contain small negativly charged particles called electrons. -
Millikan
Millikan was the creator of the Oil-Drop Experiment. He proved the mass of the electron is extremly small. Also, he confirmed electrons carry a small negative charge. Based on his data inferred he said that atoms must contain positive particles as well as negative particles. -
Ernst Rutherford
Rutherford was the creator of the Gold Foil Experiment. He said that atoms are mostly empty space, but a the center of the atom there is a tiny, dense, positively charged nucleus. Also, all of the mass of an atom is in the nucleus. -
Sir James Chadwick
Sir James Chadwick confirmed the existence of neutrons. This was detected through bombarding beryllium with alpha particles. -
Niels Bohr
Niels Bohr said electrons travel around the nucleus like planets orbit the sun.
