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400
Democritus' Theory 400 B.C.
•Stated that atoms are indivisible and indestructible
•Lacked experiments -
400
Democritus Atom Model
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John Dalton's Atomic Theaory
•Stated elements are composed of small, indivisible particles called atoms
•Atoms of the same element are identical. Atoms of different elements differ
•Atoms from different elements can mix physically or chemically to form compounds
•Chemical reactions occur when atoms are seperated from one another, joined, or rearranged
•Atoms never change into a different element
EXPERIMENTS
•experiments on ratios in which elements combine into chemical reactions -
Dalton Atom Model
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JJ Thomson's Theory
•Discovered electrons
EXPERIMENTS
•Passing electrical current through gasses at low pressure
•Tube with electrodes on the side
•Current bent -
Thomson Atom Model
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Rutherford Atom Model
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Ernest Rutherfords' Theory
•States atom is mostly empty space
•The positive charge and mass re all in one central region
•Discovered nucleus
•Nuclear Atom
EXPERIMENTS
•Gold Foil
•Source of Alpha particles beams on gold foil
•Nuclus in the gold had enough positive charge to reflect some of the particles -
Niels Bohr's Theory
•Stated that electrons move in a circular orbit at fixed distances from the nucleus -
Bohr Atom Model
