ATOMIC TIMELINE

20TH CENTURY- MODERN THEORY

• Electrons are found in electronic clouds, not paths
• Electron paths cannot be predicted

1913- BOHR

• Electrons travel in definite paths
• Electrons jump between levels from path to path

1911-RUTHERFORD

• He conducted the gold foil experiment
• Atoms contain mostly empty space
• Most of an atom's mass is in the nucleous
• There is a small, dense, positively charged nucleous
• Electrons move in empty space in the atom

1897- THOMPSON

• There are small, negatively charged particles inside an atom
• He conducted the cathode-ray tube experiment
• His theory of atomic structure led to the "plum pudding" model

1803-DALTON

• Atoms of the same element are exactly alike
• Atoms of different elements are different
• Element combine in specific proportions
• He conducted experiments in combing elements

440 B.C. DEMOCRITUS

• Atoms are small hard particles
• Atoms are "uncuttable"
• Atoms constantly move
• All substances are made of atoms