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200
Democritus
tIn 400 B.C. Democritus, another greek philosipher, belived that the universe was made up of small, indivisible spheres, called atomos. -
Lavoisier
Lavoisier made chemical changes, and measured there masses in a sealed container. Since the starting mass and the end mass was the same, he created the Law of Conservation of mass. This stated that matter can't be created or destroyed. -
Proust
Proust dixcovered that same compounds contain the same make-up. Water has 89% Oxygen and 11% Hydrogen. This is the Law of Definite Proportion. -
Dalton
Dalton took other people's work and calls it his own. Dalton came up with the Atomic Theory. He stated that matter is composed of tiny, indivisible particles called atoms, atoms of the same element are identical, and atoms of any one element are different from those of another element, Matter can't be created or destroyed, but reactions can occur, and finally, he stated the law of definite proportion, and the law of multiple proportion. -
Thomson
Thomson discovered that atoms are made up of tiny positive and negative particles called protons and electrons. He did this by using a cathode ray tube. -
Rutherford
Rutherford did a gold foil experiment where he shot positive alpha particles at a peice of gold foil. The majority of the particles went through, but some were deflected. This meant that atoms must be a lot of empty space, with a small dense center. Also, the small dense center must be positively charged since the particles were deflecting right back at the stream of particles coming in. -
Milikan
Robert Milikan used the oil drop experiment to discover the charge of a electron, which is negative. He did this by dropping oil through a small whole, and putting x-rays into the chamber. He then used magnetically charged plates to make them rise or fall or even float. By this he determined the charge of an electron. -
Chadwick
Chadwick discovered the nuetron by realizing that atoms of neon have different masses. So, atoms must be made up of particles that have mass, but not any charge. -
Period: to
The History of the Atom up until 1932
