ELECTRONIC TIMELINE

20TH CENTURY

• Modern theory
• Electron paths cannot be predicted.
• Electrons are found in electron clouds, not paths.

1913

• Bohr's theory
• Electrons travel in definite paths.
• Electrons jump between levels from path to path

1911- RUTHERFORD'S THEORY

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

1897- THOMSON'S THEORY

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

1803- DALTON'S THEORY

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

440 B.C.- DEMOCRITUS

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