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460
460 B.C.E.
Democritus, a Greek Philosopher, developed the idea of atoms. He asked the question that basically states: Can you cut an atom in half over and over again until it's physically impossible? He thought it did end at some point but the great Aristotle went against his idea and said it was worthless. Since Aristotle was very idolized people would bandwagon into his opinions. -
1800's
English Scientist John Dalton came up with an original idea of what atoms were. The following are theories he came up with and ARE true:
-Everything is made up of atoms
-Atoms of different elements are different
-Atoms can't be broken (chemical reaction only)
-Atoms combine in whole number ratios to form compounds
-In chemical reactions, atoms are rearranged -
1897
English Physicist, J.J. Thomson discovered the electron and announced a model for the structure of the atom. He knew atoms were negatively charged so he thought, they must be positively charged. His model was called "Plum Pudding." -
1911
Ernest Rutherford; interesting to prove to bombard atoms with alpha rays to investigate the inside of an atom. Used radium as source for alpha particles. Performed experiment by having gold foil get the alpha particles shinned on it. The results were much different from his expected result. It represented alpha particles had to be scatttered by small bits of positive charged matter. Though electroms were amon the empty space. He thought the negative electrons orbited a positive center. -
1913
Danish physicist; Niels Bohr. He came up with a theory of rules of what happens to an atom.
Rule 1: Electrons can orbit only at certain allowed distances from nucleus
Rule 2: Photos emit whenever an electron jumps from one orbit to another.
Bohr Model. -
1920
Electron Cloud Method. Electrons don't move the way planets move around the sun. Impossible to determine exact location of an electron. Diagram is a density diagram. Most dense to less.
